Apple on Tuesday was forced again to delay estimated shipping times for new iPad 2 orders, as those who buy must now wait four to five weeks for their order to be sent.

Yet another delay comes as stock of the iPad 2 around the U.S. is believed to be entirely sold out at all locations, including Apple’s retail stores and partners. Some select Apple stores with new shipments of the iPad 2 are set to open early today, while many other stores await more stock in the face of crushing demand.

The latest delay applies to all models of the iPad 2, including Wi-Fi and both 3G models from AT&T and Verizon. It also includes all capacities: 16GB, 32GB and 64GB.

“Demand for the next generation iPad 2 has been amazing,” Apple said in a statement to the press this week. “We are working hard to get iPad 2 into the hands of every customer who wants one as quickly as possible.”

Tuesday’s need to push back estimated shipping times is the latest in a string of delays since the iPad 2 first went on sale in the U.S. last Friday. Initial orders were scheduled to ship in a matter of days, but the wait was quickly pushed back to between two and three weeks.

On Saturday, Apple was forced to extend estimates to three to four weeks. Now, customers who hesitated to buy could be waiting over a month to receive their iPad 2.

Wall Street analysts generally expect that Apple sold at least a half million of the iPad 2 in its first weekend of availability. More bullish estimates have forecast Apple to have sold as many as 1 million at launch.

The first reviews of the iPad 2 have emerged, declaring Apple’s new touchscreen tablet as even farther ahead of its competitors than the original iPad, though some reviewers were disappointed with the image quality of the device’s new front- and rear-facing cameras.

The iPad 2 sports several new evolutionary enhancements both inside and outside. On the outside, the tablet is thinner, has a flat back with tapered edges and a front-facing VGA camera and a rear-facing HD camera. Internally, Apple has upgraded the original A4 processor to a dual-core A5 chip with significantly faster graphics.

The device goes on sale on March 11 at 5 p.m. and starts at $499 for the entry-level 16GB Wi-Fi version.

Reviewers were impressed with the changes Apple made to the iPad, though minor complaints ranged from poor image quality on the cameras to the lack of Adobe Flash and 4G connectivity.

Wall Street analysts have reported being impressed by Apple’s new iPad, with one analyst warning that the success of the iPad 2 could burst a bubble for its rivals in the tablet market.

The Wall Street Journal

In his review for The Wall Street Journal, Walt Mossberg found improvements to the device to be “generally pleasing and positive,” noting that the tablet “worked very well” for him.

For Mossberg, evolutionary enhancements made to the second-generation iPad outweigh any drawbacks or feature omissions. “For most average, nontechie users, I would recommend it over the handful of tablet competitors I’ve tested so far, especially given that the entry price remains attractive,” Mossberg wrote.

“The iPad 2, in my view, offers an excellent balance of size, functionality and price, and keeps Apple ahead in the tablet race, at least for now,” he continued. However, Mossberg doesn’t advise current owners of the iPad to “race to get the new version,” since he sees nothing particularly “revolutionary” about the new iPad.

Mossberg found the new iPad 2 to be “airier” and noticeably lighter. The device “felt very snappy,” with apps launching and running “a bit quicker” than on the first-generation iPad. And, unlike the reviewer’s tests with Android tablets, the iPad 2 never crashed in his tests.

Mossberg found still photos taken by the iPad 2 to be mediocre and battery life to be slightly less than the original iPad, though still above 10 hours. Another drawback to the device was that the new tapered edges make the dock connector port more difficult to use.

The reviewer also missed the lack of Adobe Flash compatibility and the fact that the iPad 2 will be unable to take advantage of 4G cellular data networks.

In spite of these drawbacks and omissions, Mossberg said he can “comfortably recommend it as the best tablet for average consumers.”

The New York Times

The New York Times reviewer David Pogue wrote that the iPad experience had been transformed by Apple’s improvements in thinness, weight and speed.

At just 0.33 inches thick, the iPad 2 makes the Motorola Xoom tablet look “obese,” said Pogue, who views the iPad’s success as a function of its emotional appeal, rather than its ‘on paper’ qualifications.

Pogue also spent ample time praising Apple’s new Smart Cover as “a perfect symbol of its fondness for high-tech magic tricks.”

Even as dozens of rival tablets are set to hit the market in the coming months, Pogue believes “the iPad will still dominate the market, because it dominates in all the most important criteria: thinness, weight, integration, beauty — and apps.”

According to Pogue, Apple’s aggressive pricing could help the iPad maker stay ahead of the competition. Despite Apple’s usual reputation for costing more than its competitors, “the iPad 2 actually costs less than its comparably equipped Android rivals, like the Xoom and the Samsung Galaxy Tab,” Pogue noted.

Associated Press

AP Technology Writer Rachel Metz wrote that Apple, with the iPad 2, “is pulling further ahead” of its competitors, even as numerous companies are trying to catch up to the original iPad.

According to Metz, Apple’s improvements “make an already excellent tablet even more enticing,” revealing that the iPad maker “refuses to be bested.”

The iPad 2′s “sleeker lighter body with a curved back” help the device “fit more naturally” in the reviewer’s hands, making it “easier to hold for extended e-reading sessions.”

Metz enjoyed the addition of front- and rear-facing cameras and Apple’s FaceTime video chat application, though she did find still photography “awkward given the tablet’s size.”

After spending time with the new GarageBand app for the iPad 2, Metz “was wowed by how simple it was and how well it took advantage of the iPad’s touch screen.”

Metz did find herself wishing for a second speaker, but noted that the lone speaker “did sound quite crisp, even with the sound turned all the way up.”

Metz concluded by saying that the iPad 2 is, without question, a “great tablet,” while recommending that those looking for the latest and greatest should “go for it.” “Chances are, it will be the best tablet in town — at least until the iPad 3 arrives,” she quipped.

According to one Wall Street analyst, Apple’s soon-to-be-released iPad 2 could burst a bubble for competitors who are hoping to capitalize on the growing tablet market but remain unable to catch up.

Analyst Mark Moskowitz of J.P. Morgan Research warned investors early Wednesday that build plans for tablet shipments from Apple’s rivals may be too high, presenting “increasing risk of a bubble burst” in the second half of 2011.

“In our view, the technical and form factor improvements of the iPad 2 stand to make it tougher for the first generation of competitive offerings to play catch-up, meaning actual shipments could fall well short of plan,” Moskowitz wrote.

Using discounted build plan estimates to project tablet shipments for the year, the analyst claims that tablet makers will build approximately 65.1 million tablets in 2011. When compared against J.P. Morgan’s estimates of 47.9 million tablets sold this year, companies could find themselves with as much as 51 percent oversupply in a worst case scenario.

Apple is expected to maintain the lion’s share of the tablet market. Moskowitz estimates that Apple could see nearly 100 percent sales growth year over year, resulting in more than 29 million iPads sold worldwide in 2011.

According to Moskowitz, component suppliers could stand the most to lose from a bubble burst. “Based on our research inputs, tablet makers eager to emulate Apple’s meteoric start are trying to secure components with inflated build plans,” Moskowitz noted. “Of note, glass displays, processors, and, to a lesser extent, NAND Flash are the components that could be most at risk.”

Moskowitz has a “favorable view of Apple’s products and operating model,” but acknowledges that “Apple is not for everyone.” However, holdouts hoping for an alternative to Apple’s iPad may be “underwhelmed” by rival offerings.

“Aside from Motorola’s Xoom and HP’s TouchPad (which does not have a price tag yet), the competitive offerings appear to be light on attraction, in our view,” said Moskowitz.

J.P. Morgan maintains an Overweight rating on Apple with a price target of $450.

Initial Wall Street response to the unveiling of the iPad 2 last week has been favorable. In general, analysts were impressed by what were seen as “evolutionary” upgrades to the device and the thinner and lighter form factor. At the time, Moskowitz admitted that his firm’s forecast of Apple holding 68 percent market share in 2011 “may be conservative” in light of the iPad 2.

Wall Street analysts reacted positively to Apple’s unveiling of the iPad 2 on Wednesday and remained optimistic about the company’s continued ability to lead the tablet market, though they viewed the refresh as mostly “evolutionary.”

As expected, Apple revealed a faster, thinner and lighter second-generation iPad, officially dubbed iPad 2, to the media at the Yerba Buena Center for the Arts in San Francisco on Wednesday. The touchscreen tablet, which sports front- and rear-facing cameras, an upgraded A5 CPU and improved graphics processing, goes on sale on March 11.

Though Wall Street analysts admitted that Wednesday’s event contained few surprises, they remained confident that several key “evolutionary” upgrades and the addition of new content production apps to the iPad would continue to drive growth for Apple.

Boosted by investor confidence in both the iPad 2 and a surprise onstage appearance by Apple CEO Steve Jobs, shares of Apple closed the day up .80 percent at $352.12.

RBC Capital Markets

For analyst Mike Abramsky with RBC Capital Markets, the slimmer form factor and ‘Smart Covers’ magnetic cases demonstrate the design innovation that Apple needs to sustain leadership in the tablet market, while evolutionary like FaceTime cameras, an HDMI-out accessory and a dual-core processor will keep the pressure on Apple’s competitors.

Abramsky viewed Jobs’ appearance as a “welcome surprise to the event,” while noting that the other announcements and iPad 2 features were “largely inline” with expectations. According to the analyst, Apple’s milestone of 100 million iPhones sold matches sales forecasts for the quarter.

The iPad 2 will likely “drive a ‘mini’ product cycle” for Apple similar to the MacBook Air, Abramsky said in his note to investors. The March 25 international launch of the iPad 2 will also precede most “next-generation competitive tablets” to several key international markets.

“iPad 2 raises the bar and sustains pressure on competitors, and continues to target media-centric tablet consumers seeking a premium experience,” Abramsky wrote. However, according to Abramsky, the refreshed tablet from Apple doesn’t “alter competitive landscape for pending Android tablets or PlayBook, which may appeal to different market segments (like Android/Google fans, productivity-centric or enterprise segments).”

Morgan Stanley

Katy Huberty with Morgan Stanley views the iPad 2 as “an important evolutionary step in the product’s short history” that will likely serve to widen Apple’s lead in the tablet market by building on the original iPad’s “overall system, ecosystem and pricing advantage.”

The analyst noted that there were “no big surprises” at the event, though she did notice “dramatic performance improvements,” especially with webpage loading speeds, and an improved user experience during a hands on demo with the new device.

Huberty predicts a high adoption rate of the “Smart Covers,” which could partially offset the second-generation tablet’s presumably higher bill of materials.

According to the analyst, the March 11 ship date for the iPad 2 was “faster than expected” and could help Apple to continue widening its lead on competitors.

JP Morgan

In a note to investors, JP Morgan’s Mark Moskowitz suggested that the firm’s forecast of Apple holding 68 percent of the tablet market in 2011 “may be conservative” in light of Wednesday’s iPad 2 rollout.

The analyst found it “suitably impressive” that Apple is already launching a second-generation iPad “just as the competition is rolling out or prototyping their first-generation tablets.” The analyst also sees new interactive applications, such as iMovie, GarageBand and FaceTime, as likely drivers of growth among younger consumers.

Moskowitz called Apple’s technical and form factor improvements “more than good enough,” given that competing companies are viewed as bringing tablets with “higher price points or clumsier form factor/technical specs” to market.

Sustained growth of the iPhone, especially in China, will help Apple to maintain a 25 to 30 percent growth rate in earnings through 2015, says investment firm Piper Jaffray.

Analyst Gene Munster issued a note to investors on Wednesday expressing the belief that Wall Street currently underestimates Apple’s mobile growth potential. Piper Jaffray’s 12 month price target for Apple stock is $483. According to Munster, if the iPhone can continue to grow in-line with the smartphone market at a rate of roughly 35 percent in calendar 2011, Apple will sell over 200 million iPhones in 2015.

Given that the iPhone currently comprises 39 percent of Apple’s business and that the iPad will likely grow faster than the iPhone, Apple is expected to achieve a sustainable 25 to 30 percent growth rate in earnings.

Piper Jaffray’s growth rate estimate runs significantly higher than some of its Wall Street counterparts. “Most investors believe Apple’s earnings growth will slow to 15-20% in 2012,” said Munster in his note.

With the advent of the iPhone 4 on Verizon, Apple no longer carries any exclusive arrangements with carriers. Munster sees this as a meaningful opportunity for the iPhone maker to add to its addressable subscriber base in “critical markets.”

Source: Piper Jaffray estimates

In China, for example, third-place China Telecom has nearly as many subscribers as Verizon, the largest carrier in the U.S., while Indian carrier Reliance, who is also rumored to be in line for the CDMA iPhone, has an impressive 110 million subscribers. Munster believes Apple could initiate a partnership with China Telecom and/or Reliance in 2011.

Apple identified China as a top priority for the company several years ago and has since put “enormous energy” into its expansion there. The strategy is already beginning to pay off, as revenue in Greater China, which includes mainland China, Hong Kong and Taiwan, was up 400 percent year over year in the recent quarter.

Apple’s four China-based retail stores are the company’s highest traffic and highest revenue stores. As a result, the Cupertino, Calif., company is looking to build bigger stores to accommodate the high number of customers, starting with an upcoming store in Shanghai that will reportedly be the company’s largest retail location to date.

Munster, however, is not the only analyst who sees China as critical to Apple’s continued growth. According to Ticonderoga Securities analyst Brian White, China is in the early stages of catching “Apple fever.”

Katy Huberty with Morgan Stanley is also bullish on Apple’s sustained growth in China. The country “could contribute well over half (and as much as 100%) of the total company earnings growth we expect” through fiscal 2012, Huberty wrote in a recent report.