I just ran into LibraryThing. It. Is. So. Cool.
You can quickly create a catalog of your entire personal library of books. Complete with tagging! I know this is super nerdy and only for the book lovers, but my gosh I am just digging this. This is my new timesink.
Ever since I got a Mac, I’ve been contemplating Delicious Library. No more. This’ll do. And if you’ve already got Delicious Library, you can import your data to LibraryThing!
BTW, this is me on LibraryThing (so far, I’ve just cataloged the books sitting on a table in the living room).