This [PDF] is an outstanding piece (found via Mathemagenic) about using simple visual cues to help participants get the sense of the group dynamics in an online conversation. The applications the author talks about are all synchronous but some of them could easily be adapted for an asynchronous environment. In particular, the lecture proxy and the conference call proxy could easily be used as visual feedback for different types of discussion board conversations, depending on how strongly facilitated they are.
Good stuff. (And as a bonus, there’s information about an ongoing online limerick-writing game.)