I've heard about LibraryThing for years, so nice to try it out. After adding my first five books, instantly I have a connection with a Queensland poet who has the same lovely book by poet Lydija Cvetkovic in her LibraryThing book collection.
I think this is very much a networking site -- a site for talking about books and making collections to share, not so much a site for finding out, though you can do that too.
Over the years in library work, from time to time people ask how they can make a simple catalague for the book collection of a society, for example. LibraryThing is one very easy answer.