Here’s a twist on social bookmarking…you go to the LibraryThing website and enter your book collection. Then others can see your collection and from that and collections of others, figure out what they want to read next.
Web-based data entry can take an ISBN and search LC and/or Amazon to grab the metadata about a particular book but it’s sort of slow.
Interesting idea…and for $10 you can get a lifetime account which gives unlimited title storage. If you just want to use the service for free, you’re limited to 200 titles.
When I last checked there were 45,000 titles in the database (not sure that they’re unique titles…pretty sure they’re not).