Ooh ooh ooh! I joined up with Library Thing a couple of weeks ago and it's very neat-o.
What you do is create a list of all of the books you own and others do the same. Then you can get recommendations for more books based on what others who own similar books also own. Or something that makes a bit more sense. Forgive me, it's late and I've had wine.
Or you can be nosy and just look and see what other people read. Which is what I do when I'm at someone's house--I always check out their bookshelves. You can learn more about them by scoping the books than their medicine cabinet.
Oh it's just very, well, very spiffy. I've only added a teensy portion of the books I own, but I would like to update it from time to time.
Go check it out--I'm Rational Jenn, of course.
Thanks to Aaron!