When you download a book onto your reader, it is encrypted and it will only be readable on your particular reader. So, say I read a wonderful book and want to share it with my son who lives in Berkeley. Right now, if I own the book, I drop it in the mail to him, or give it to him sometime when he's visiting. Then I won't be able to read anything else until he has finished with it and returned it to me. Even if he had his own Rocket eBook, I couldn't download it to his device.
Libraries exist on the principle of shared access.
This last involved downloading a special piece of software called the Glassbook reader. Some libraries are buying Rocket eBooks and other e-book devices, loading them with a few books, and then checking out the whole device to their users. To me, that feels a little bit like checking out a VCR with every video we circulate-cumbersome and not very efficient. There are 10,000 books in my library, and it will keep on growing until I die.