There are so many interesting relationships here. I would enjoy a search function that queried two users and parsed them for shared threads. The output would contain all the threads that both user A and user B posted to--possibly with other criteria, such as key words? If this has been suggested before, I haven't been able to find it.
Fulfilling the MetaFilter Promise. What is your vision of what the MetaFilter (and MetaTalk) project could be or should be? Those here tend to agree that this enterprise is important, so why is it so? What is MetaFilter doing and what might it do? As an exercise in originality, consider posting your ideas before reading the others. (Disclaimer: I'm writing a thesis on Blog Communities, and this one's my fave).