From Ezra Klein's article on the future of reading:
The true promise of the Kindle, and its inevitable descendants, is in creating a product that goes where the book cannot. Printed text is fundamentally limited. Once on the page, nothing more can be done with it. With digital text, everything is a draft, to be edited, altered, broadened, remixed, and redirected. As better conveyors of electronic text are developed, the big question is how content itself will change to take advantage of the new opportunities.