Here is an interesting post on design problems inherent in touchscreen-based technology (via Brent Ozar PLF’s weekly list). There is something to be said for tactile interfaces: typing on an old IBM keyboard provides much better feedback than trying to type on a similarly-sized touchscreen keyboard (not to mention a much smaller touchscreen keyboard).
The other problem that I see is that most of our daily experiences are three-dimensional in nature: the relative thickness of a book, as pointed out, tells you a pretty good amount on its own: it tells you how far along you are, roughly how much more there is to go, and how big the book is compared to other books. Without that third dimension, you need page numbers, or you’re lost. The lack of a notable third dimension certainly keeps devices portable and light (I’m not complaining about being able to store hundreds of books on my nook, and I can lay my nook flat and expect to be able to read from it without holding the thing open) but comes with some tradeoffs. When it comes to something like a keyboard, or some other device in which constant visual observation is a bad thing, the model falls apart, leaving us to cope with subpar design.