11. The first thing I noticed about Library Thing is how utterly easy it is to sign up with. You don't provide and email address, real name, country etc, just your chosen username and a password and you're done. More places should work that way!
Adding books to your profile is as simple as searching for a title or author just like we do on amazon or anywhere else - in face the book information and covers are pulled from amazon by default. If Amazon fails (for out of print books generally) there are more than 60 other places to search and if all THAT fails, you can manually enter the book into the database.
Once added, you'll see how many other people have added the same book. My "other people" numbers go from 2888 for "Hitch Hikers Guide to the Galaxy" to 2 for "The Year of the Cornflake".
The interface is really clean and intuiative, things are exactly where you'd expect them to be and it's coded in a way to make the pages load quickly. Each title has an information page including reader reviews and ratings, recommended titles and titles by the same author, which would make it handy for building a collection of, for example, Terry Pratchett.
I do notice the conversation button on the information pages is a little hit and miss, but still not a bad way to turn up forum posts. There's also a link to several (fabulously exciting imho) Book Swap services online.
My Book Thing cataloge can be found here, plus there's a widget in my sidebar.