One of my favorite apps on Facebook is WeRead. It's on the same idea as Shelfari or LibraryThing, which are websites for readers to keep track of the books they've read and include images of the book covers, book reviews and user comments.
I just enjoy the ease of WeRead because it's got the facebook app, I don't have to think about logging into a different website; I just log in once to facebook and start adding my books.

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