Web site Shelfari lets you build your own virtual bookshelf, then
create a social network where you and your friends can review, tag, and
recommend books.
Shelfari makes it easy to add and manage books in your library, and
if you’re an avid reader, it looks like a potentially great place to
find and share good books. You can also indicate which books in your
library you’re currently reading, so if you have Shelfari friends who
are also friends in the physical world, this is a great way to find and
borrow books. If you’re looking for a more robust system for trading
books online, check out previously-posted PaperBackSwap or BookMooch.