Chris Allen has a deeply researched post, Dunbar, Altruistic Punishment, and Meta-Moderation, which deserves a close look: "In summary this research offers me another widget for my social software toolbox: in any group process look for the commons, allow participants to participate in identifing defectors; determine what the costs are for such identification (which may be as simple as requiring some attention or charging for such punishment); and encourage participation in the common good by punishing those who do not participate in seeking out defectors."