Michael Castor, the Product Curator and Evangelist for MakerMedia, decided to make a PiPad using a $40 Raspberry Pi Model B, Revision 2.0 for its core. This credit-card sized system board uses the Broadcom BCM2835 system on a chip (SoC). This in turn uses an ARM1176JZF-S 700MHZ processor. Yes, it's not fast. It also includes an on-board HF-capable VideoCore IV GPU capable of High-Definition video playback and has 512 megabytes of RAM. An SD card is used for booting and long term storage.
Castor's design goal was to create a "simplistic, functional design … I enjoy fun, hidden features. … I thought about hollowing out a book and putting it in there (like Penny’s book computer from Inspector Gadget) but decided to go with a stand-alone tablet form-factor. Since I wanted to let the PiPad keep me company on flights, the enclosure had to look as factory as possible, while remaining accessible and usable. The last thing I want is for it to freak out the TSA or the old lady sitting next to me."
He then designed the system with Vectric’s Aspire CAD/CAM package. Next, he built it by hand and exacto knife. As is always the case with such things, it didn't work perfectly at first. The screen proved wonky because the board was touching other components. After some surgery on the board, it worked just fine.
So, can you make the equivalent of an Apple iPad or a Nexus 7 with a Raspberry Pi? Nope. But, you can still create your own tablet, your own way, if you follow Caster's instructions. Good luck and good building.