I’ve talked with friends before about a Netflix-like service where you could mail in a book and get a new one sent to you. The obvious limitation is that a book weighs significantly more than a DVD.
Now Amazon is in talks about renting ebooks to readers.
I wonder how this will fare, considering gutenberg.org and a number of other sites offer free books for keeps. Public libraries also offer free ebooks for a time, like the Southeast Regional Library’s Overdrive service. I guess it will come down to an issue of cost versus selection.