Maybe have it based around users of some renown, based on post count, account age or something, and to make a player ban effective, it needs at least three "votes" to be effective? 

Mind you, that'd still need a safety net to prevent a group from taking out others in anger. Perhaps the ability could be revoked if abused
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As for timer for delays, maybe increasing delay if posts are too quick? Or something to check for identical posts on newer users?