Yet another addition to the list of Web sites I thought up then realized someone had already built (this happens a lot): LibraryThing.
Genius in its simplicity, LibraryThing lets you catalogue your personal
library of books using Amazon and Library of Congress cross-checking to
dedupe the list, avoiding many of the problems a site like this could
endure. Once entered, you can tag and review your titles, and it spins
out all the usual Flickr-style tag clouds for finding popular or
interesting titles, authors, and genres. I don't know if its better that Reader2, which does some of the same things for reading lists rather than personal collections, but it's pretty good.
If Amazon doesn't end up buying this site, I'd love to see the CNET
mothership grab it and give it the Gamespot/TV.com/MP3.com treatment.
There's some real potential here. Now, if only they had a version for comic books...