We've been extremely successful with our paid membership system.
It began on Sept. 1st, and we are getting actually MORE posting traffic than we had when we were free.
We charge $5 for 3 months or $15/year. I created the hacks that integrated with our Merchant account at Wells Fargo through Authorize.net.
Everyone can view messages, but only paid members can post, use priv. msging and go into chat. We have 4 "members-only" boards that are only viewable to paid members.
I am available for hire if anyone wants me to convert their board!
Jennifer.