A lot of the newer kindle books are packed full of multimedia features and you will only be able to take full advantage of them with the new application for iPhones, iPads, and the iPod Touch.
Adding music or narration to digital editions of books might be the next big thing by giving users the choice to either read or or listen to the story. I still question the need for videos with a book though.
Is it still considered a "book" if there is video?