"Kindle Maths 101," by Ben Vershbow at if:book:
Do we really need an iPod for books? / We might, maybe (putting aside for the moment objections to the ultra-proprietary nature of the Kindle), if Amazon were to abandon the per copy idea altogether and go for a subscription model. (I'm just thinking out loud here — tell me how you'd adjust this.) Let's say 40 bucks a month for full online access to the entire Amazon digital library, along with every major newspaper, magazine and blog. You'd have the basic cable option: all books accessible and searchable in full, as well as popular feedback functions like reviews and Listmania. If you want to mark a book up, share notes with other readers, clip quotes, save an offline copy, you could go "premium" for a buck or two per title (not unlike the current Upgrade option, although cheaper). Certain blockbuster titles or fancy multimedia pieces (once the Kindle's screen improves) might be premium access only — like HBO or Showtime. Amazon could market other services such as book groups, networked classroom editions, book disaggregation for custom assembled print-on-demand editions or course packs.
Vershbow also quotes Tim O'Reilly:
Unlike music, which is quickly consumed (a song takes 3 to 4 minutes to listen to, and price elasticity does have an impact on whether you try a new song or listen to an old one again), many types of books require a substantial time commitment, and having more books available more cheaply doesn't mean any more books read. Regular readers already often have huge piles of unread books, as we end up buying more than we have time for. Time, not price, is the limiting factor.