LibraryThing is great. I especially liked its recent integration into public library catalogs, like Danbury. Seeing the additional info they provide within a record, like similar books, tags and patron reviews, is fantastic. We're definitely seeing the next wave of OPACs.
It's interesting how public and some school libraries are using LibraryThing for reader's advisory (I'm doing this now) and to promote new books. This can be done quite easily. You just export ISBNs of books you've added within a date range (which can easily be done with our circ system Alexandria), upload to LibraryThing, and tag them new books. I tried this with a file of about 40 and it was quite quick for them to process; depends how many others are in the queue ahead of you. See the widget on my blog. One concern I have is the social networking aspect, the book sharing conversation between students and adult LibraryThing users. That's the challenge with Web 2.0, teaching students how to use the Internet safely and appropriately.