Social bookmarking for books

Shelfari is a social network and recommendation service that lets you flaunt your book collection to others, and discover new titles worth reading. Yesterday Shelfari announced a round of funding, with Amazon.com being the top contributor.
If you've ever seen Delicious Monster, Shelfari is visually similar, with virtual bookshelves that house your collection as long as you're willing to manually input all your titles. The result is a slick-looking listing to share with others on your blog or Web site (see below), and make friends with people who have similar tastes to swap recommendations.
Each Shelfari book page is essentially an extension of what you'd find on Amazon.com, with buyer reviews and a five-star rating system. Shelfari employs a fair bit of Amazon.com integration, using Amazon's comments and purchasing options. Clicking the option to buy the book actually takes you off-site to the book's page on Amazon.
From a user perspective, Shelfari's real draw is groups. Users can create their own groups based on very specific genres, like "banned books" or "19th century English literature." Each group has a common shelf, where users can contribute titles. There's also an attached forum for discussion, and an introductory page with room for a description and any worthwhile URLs.
Shelfari is a great way to pick up book recommendations. I often find books worth reading through friends, so it's only natural to have a social network that fosters a similar service. But there's still something to be said about exploring a bookstore, which despite its good looks, Shelfari can't match.