Amazon

Unveils the Netflix for books - Kindle Library.

This is pretty frigging awesome.

UPDATE: I could envision a next iteration where you rent books. Why not? You could even price them differently. And really - why do we buy books anyway? The vast majority, after you read them, you don't go back. Rare are the books really worth owning. Such a system would be more accurate to the actual value of books. Of course, you could still buy the good ones.