Neat...but...
Interesting idea, but would be great if I could actually in-app-borrow a friends book. I suppose there are some fundamental problems (copyright etc), but if you limit shared books to online purchased books (which brings up something else), and limit ownership to the original purchaser (eg: the book is automatically returned/deleted/self destructs after x days).
This app is sort of like a video-phone. Its a neat idea, but, until all my friends get one, do I really need it? I know which books I own... I dont really need to catalogue my own, unless I want to lend them to a friend... oh, but they dont have an iphone/ipod touch/ipad so how can I share my list?
The other thing this brings up is, why not make it possible to in-app-purchase a book (eg from an online digital book source) and download it directly to my iTouch/iphone/ipad.
Lao-Tse about
iBookshelf Lite