You can see some of the technical challenges involved in the multimedia-digital-book idea by checking this out: an approach to William Blake called “Songs of Imagination and Digitisation.” I love the Future of the Book people, but this just doesn't strike me as a promising endeavor. As I browse through this I get (a) intentionally “jumpy” page backgrounds, presumably meant to give a sense of energy and action; (b) low-resolution audio/videos of talking heads saying just a few words at a time, reading poems (some of them split into multiple videos) or giving historical background; (c) texts of poems; (d) a few images.
This is all done in Flash, and there’s clearly an awareness of bandwidth limitations — thus the brevity of the videos. But I wonder how much bandwidth would be necessary in order to give us Blake’s work in proper fullness and resolution — along the lines of what you get on a CD like this one, from Octavo. An Octavo CD doesn't give you the videos or the sounds, and you have to pay for it, and you can't access it online — but it’s the closest thing to having Blake’s poems as he meant for us to have them, in their full illuminated vibrancy. And if you are determined to have free and online access, I would recommend the Blake Archive. Flash is good for some things, but I don't think “Songs of Imagination and Digitisation” is, after all, the future of the book.