Now that you can "loan" e-books from your Kindle or Nook, eBook Exchange is setting up a database allowing users to register and lend books to strangers:
List your ebooks for others.
eBook Exchange™ is the primary lending and borrowing marketplace for Kindle™ and Nook™ ebooks. Once you've read an ebook, put that purchase to work rather than letting it stagnate in your e-reader's archives.
Borrow today's best selling ebooks.
It's never been easier to discover new authors writing today's bestsellers. Start now by registering, for free.
I wonder if Amazon or B&N will try to put a stop to this? It probably helps eBook Exchange's odds of survival that the FAQ points out that all profits go to childhood literacy programs.