The best thing I've seen forum-wise has been strict moderators who also post. They're part of the community, so you actually care about whether or not you upset them. It takes a lot of work, but it's worth it.

Karma is for community evaluation of someone's contributions -- "is this person good to learn from?" Moderation is to punish dickish behavior, bad argumentative habits, etc. Moderation can have an element of authoritarian caprice, which is actually good for morale, like a well-loved grade-school teacher with her own strict, quirky rules.