As anyone who's ever moderated a large forum can tell you, playing with incentives works almost embarrassingly well and quickly compared to working on sympathy or respect for authority. Of course, it's also harder to do.

That sounds very intriguing. Can you give some example of how you've used "playing with incentives" successfully to (I assume - correct me if I'm wrong) maintain a productive forum? That might be very enlightening - seriously, no irony here.