The introduction of the iPad Friday morning sold an estimated 50,000 units in two hours, and also bumped Apple's "hobby," the Apple TV, from the front page of its online store. Also, a mysterious icon included in iPad promotional pictures gains attention, and Apple has expanded its site to explain features of the coming hardware in greater detail.

iPad sales estimated at 25,000 per hour

After it went on sale at 8:30 a.m. Eastern Friday, the iPad is estimated to have sold 51,000 in its first two hours. As discovered by Philip Elmer-DeWitt at Fortune Brainstorm Tech, users at the Investor Village AAPL Sanity Board took their order numbers and attempted to crack the code to figure out total sales.

Victor Castroll, analyst with Valcent Financial Group and member of the AAPL Sanity Board, has been monitoring the spreadsheet and came up with the calculation of 51,000 units in the first two hours.

iPad preorder bumps Apple TV from front page of online store

In accepting preorders for the iPad on Friday, Apple made some minor adjustments to the front page of its online store. As a result, the Apple TV product and its accompanying picture were bumped and are no longer featured atop the store's main page.

The Apple TV used to be featured prominently alongside the company's line iPods, the iPhone and Macs. Now users must scroll down and find it in the left column under the "For iPod" heading.

Last month, Apple Chief Operating Officer Tim Cook said his company still views the Apple TV as a "hobby," and noted that sales of the product simply don't compare to the consumer markets for smartphones, computers and MP3 players. Cook said he doesn't believe the Apple TV will remain dormant, but it may take time for the potential market for the device to grow.

"Because our gut says something is there, we're continuing to invest in this," Cook said. "But today, it's still just a hobby."

Last October, Apple released the 3.0 software update for Apple TV, featuring a redesigned main menu that made navigating content simpler and faster. It also added support for the new iTunes LP and iTunes Extras formats.

Mysterious app icon gains attention

Apple updated its Web site with new pictures of the iPad Friday, and one screenshot in particular garnered attention from readers due to its inclusion of a mysterious icon. Included on the home screen Web page, the picture shows an icon on the far right of the device in landscape mode, and the application is not shown in any other screenshots.

Though the text is too small to read clearly, the icon appears to show the logo for the publication National Geographic. It's likely that the icon is for a digital version of the magazine, to be sold through Apple's iBookstore.

Apple expands on iPad features

As preorders began Friday, Apple also fleshed out the official iPad section of its Web site, adding greater detail on the iBooks application, 3G data subscriptions with AT&T, and more.

As before, all of the built-in applications on the iPad have their own page describing their function. Apple also has special dedicated pages for the iBooks application, which must be downloaded from the App Store, as well as the $9.99 Keynote, Pages and Numbers software.

A page devoted to 3G access on the iPad describes how users can start and cancel a no-contract data plan with AT&T direct from the device at any time. As was revealed at the product's unveiling, the data plans run $15 per month for 250MB of data, or $30 per month for unlimited access.