Metafilter has been successful, I believe primarily due to the $5 charge to create a posting account and the warmup period of limitations for new accounts. New accounts trickle in at a manageable level. All account owners get that sense of ownership and care that comes with exchanging currency for something. Most internet brigading can't scale a small expense to begin with, and existing account owners who might otherwise get bootstrapped into a brigade don't want to get kicked out for being a jerk.