I just read about this effort on the part of LibraryThing to help St. John's Episcopal Church in Boston catalog their collection of books. I think this is a fantastic idea, and something that it would be really interesting to see done in other places.
For instance, I can imagine a cataloging class taking on the collection of a small non-profit as part of their final project. Or perhaps one of the many library association chapters that exist most places could do a similar pizza-and-cataloging party on a Saturday. They wouldn't have to use LibraryThing, any database or cataloging software would do, and the results would be really helpful for the non-profit since they would have better access to their own resources.
Hmm... I wonder if it would be possible to set up something like this. I guess the major issue would be finding a place with a lot of books that aren't already cataloged but should be.