Gene Smith has some good points and an outline or a tagging paper he’s working on: Taxonomy of tagging systems (Atomiq)
It’s worthwhile to think about how the interfaces, features and even the incentives (“it’s the user stupid”) can influence a tagging system’s design and use.
That’s actually a paper by some Yahoo! Research folks like Cameron Marlowe. Reading the paper I was sort of confused about the methods they used for the taxonomy of user behavior. They pull tag data out of Flickr and del.icio.us, but I don’t see how they can make such detailed claims about user motivations w/o actually talking to users.