To clarify: Social bookmarks? You create a group and invite people to it and everyone can see the bookmarks that are placed into the group?

This sounds like a great add-on to a social network, but not something that I'd sign up for as a standalone product.

Also, a Wiki can do that already, as long as browser integration isn't required.

If we're talking browser integration, there'd need to be some way to sync it with the server. That might be useful, if you can join multiple groups.