Shelfari is a web site containing a community-powered encyclopedia for book lovers. It is supported by Amazon and the latest Amazon Kindle devices can make use of this data. You can create a virtual bookshelf, discover new books, connect with friends and learn more about your favorite books – all for free.
(from wikipedia) Shelfari is a social cataloging website for books. Shelfari users build virtual bookshelves of the titles they own or have read, and can rate, review, tag, and discuss their books. Users can also create groups that other members may join, create discussions, and talk about books, or other topics. Recommendations can be sent to friends on the site for what books to read.