I commented this, but I think it is relevant to how we design for screen.

http://craigmod.com/journal/ipad_and_books/

The most interesting part of the article is about content.. Formless content and Definite content..

how do they relate, and how do you take the content we are familiar with in books, and translate it (the same content) in a way that is it understood in a new medium? but so it works for that medium to it’s full advantage..

“in the context of the book as an object, the key difference between Formless and Definite Content is the interaction between the content and the page. Formless Content doesn’t see the page or its boundaries. Whereas Definite Content is not only aware of the page, but embraces it. It edits, shifts and resizes itself to fit the page. In a sense, Definite Content approaches the page as a canvas — something with dimensions and limitations — and leverages these attributes to both elevate the object and the content to a more complete whole.

Put very simply, Formless Content is unaware of the container. Definite Content embraces the container as a canvas. Formless content is usually only text. Definite content usually has some visual elements along with text.”

the ipad totally shifts the idea, is it easier to read a book on screen?

you make your own opinion.