I've noted before that textbooks as ebooks would suck, mostly because you just can't flick through the pages as quickly, glimpsing dozens per second until you see what you were looking for. In an ebook, it's page-by-page flick, flick, flick, maybe two pages per second, which gets tedious very quickly. There are advantages to having digital textbooks, but the usability needs to be addressed.
It turns out that's not too hard. You could have a function for digital textbooks to zoom out so that you can see thumbnail versions of lots of pages at once and flick through them that way, then zoom back in when you find what you're looking for. I'm sure someone is working hard on the problems of digital textbooks and soon enough they will be the standard rather than the experimental novelty.
Mokalus of Borg
PS - Next problem: note taking.
PPS - Not as critical and not as hard either.