Ricky has recently published two articles on this subject with regard to the iPad. The first, by Ricky herself, suggests that its simplicity compared to a desktop OS may make it easier to learn for both cognitively impaired users and the elderly. On top of that. the availability of external keyboards helps blind users who can touch-type and cannot see the onscreen keypad, and its larger size compared to the existing touch devices will make things easier for those with fine motor issues, particularly on "upsized" iPhone apps.
Also, Paul Natsch, a quadriplegic, offers tips on how to use the touch-screen when you have limited (or no) arm function. It involves the use of the Pogo stylus. "Ultimately the iPad is probably going to be able to do quite a bit more than the iPod Touch but the iPod Touch is still essentially the iPad's 'little brother'", he writes, "So I thought I'd share the methods I use to access my iPod Touch in hopes that these ideas may be useful for people with physical disabilities hoping to get an iPad."