I like the way they use tagging at 43things, although I haven’t looked closely enough to find out exactly how they’re doing it. I think it could be useful in a library, maybe for finding out what users want most from their library or community and why. It would, at least, be more fun than taking a survey.
If you stumble upon interesting uses of tags/bookmarks, please leave a comment. And, let us know your ideas for applying any of them to libraries.