I really like Library Thing. As a cataloguer, I love that Library Thing allows me to tag books with subjects I think are appropriate, rather than being limited by Library of Congress rules. These rules state, for instance, that a kids books about Australian animals should have the subject ‘Zoology – Australian’ rather than the far-more-user-friendly ‘Australian animals’.
I have added, tagged and rated all the books I’ve read so far this year (29 and counting), and I think I will continue to use this resource in the future.
My Library Thing books can be viewed here.