As I understand..... it is for sharing files on the internet. So you don't have to email them back and forth. You set up an account and people can just log in and grab the books they want. I am learning more about it and was wondering if anyone was using it. I think you MAY still have to add a person's email but after that then they can just go in an access your book files? I am reading more about it now.
http://www.dropbox.com/