The backlog affects orders placed in the markets where the new iPad is available first -- the U.S., U.K., France, Japan, Germany, Switzerland, Australia, and Hong Kong. Apple's U.S. carrier partners, AT&T and Verizon Wireless, are taking customers' e-mail addresses for later notification when units are available. There is a limit of two units per customer .

'Off the Charts'

In a statement, Apple said that "customer response to the new iPad has been off the charts and the quantity available for pre-order has been purchased." The company noted that customers can continue to order online and receive an estimated delivery date.

The rush to buy matches many other Apple product releases, including the iPad 2, whose available supplies sold out on the first day they were available. Similarly, the most recent iPhone, the 4S, sold out in less than a day after its debut in the fall of 2011.

To this point, Apple has sold about 55 million iPads, and expectations are for that number to double by the end of this year.

Some industry observers have speculated that the new high-resolution, 2048 x 1536 screen of the new iPad is contributing to supply shortages, since the screens -- which appear to be the key attraction of the new version -- are more difficult to manufacture. The iPad 2, by contrast, offers a 1024 x 768 screen.

Even before the unveiling of the new iPad last Wednesday, there were estimates by analysts that there would be product shortages for as long as five or six months. In addition to HD screen manufacturing time, another factor is that the iPad 2 is still being made and sold, meaning that the newest iPad must share manufacturing facilities with its older sibling.

'Improvement Is Not Subtle'

The HD screen has been getting strongly positive reactions. The screen's dpi, or dots per inch, is an impressive 326. A dpi of 300 or greater is considered a "retina display," when the human eye, at a distance of about a foot, cannot distinguish individual pixels. Previously, retina displays were only available from Apple on the iPhone 4 and 4S.

Avi Greengart, an analyst with industry research firm Current Analysis, said this sell-out shows "tremendous demand for a tremendous product," and that he was not surprised "one bit."

He added that the new iPad display is so "extraordinary" that it completely changes the experience of using the device. "Everything looks printed," Greengart said, adding that the "improvement is not subtle."

He also noted that "anyone who has crazy conspiracy notions that Apple is deliberately holding back supply doesn't understand how capitalism works," since the company wants to "sell as many as they possibly can."

Aside from the attraction of the HD screen, the latest iPad also features an A5X dual-core processor with a quad-core graphics processor, a rear camera that has been upped to a 5-megapixel sensor, a new voice dictation app, plus models that support 4G LTE high-speed data connectivity.

Mathew K J:

Ryan:

Ike: