Immediately following Apple's Education Event, I downloaded a couple textbooks from the iBookstore, namely, Geometry and Chemistry. I've done some browsing and am very impressed with what Apple and the publishers have done with these textbooks.
On the surface, the books look like typical textbooks, but a simple touch brings the pages to life. You can enlarge images, flip through slideshows, watch videos and examples, take sample quizzes, and more. One of my favorites features is that there are flashcards pre-created with all the terms and definitions from each chapter. You can also create your own cards from highlighted text and user-created notes.
This is just the beginning of textbooks in the iBookstore and I'm looking forward to seeing how this all plays out.