As readers here know I still have some doubts about how desirable "enhanced" e-books are going to be. Nonetheless, as with any medium, innovative people will use platforms like the iPad to create some nifty new content (whether that content is really "books" is another question). One of the most delightful things I have seen amid the iPad frenzy is this specially adapted version of Alice in Wonderland, which is now available as a separate app in the App Store.
This may not be as satisfying for a first-time reader as simply sitting with the old-fashioned printed book--but if you know the book and love Tenniel's illustrations, as I do, seeing them come to life in this way is a new sort of pleasure.
Haven't yet got my hands on an iPad long enough to do any reading, but I will soon, and will give the obligatory report on it as a reading device.
Update: Interesting article by one of Alice for iPad's creators here, on how they did it. And several other children's books for iPad are already on the market--featured in this CNET article.