Twictionary is an open PBwiki Twitter dictionary. Good mix of usefulness and twitter culture. Most of all, Twictionary is funny - check out some of these entries:

Tweature - twitter + creature. Any user or account on Twitter that is not identifiable by content as being from a human. As apposed to tweeple, a tweature is the class under which all other unclassifiables belong, including spammers, link listers, people with a small following who use twitter like a chat client exclusively for inside jokes, and any other use or service that is unreal or is impersonal.

Twitterectomy - noun - cutting twitter out of one’s life for a period of time because twitter is taking up too much of their time.