My site
http://www.limmac.org has quite a few hacks, optimizations, plugins, and custom work done. Once a user is signed up, they get additional access granted via promotions after a week + 10 posts. To a non-registered user the site and some of it's content is still viewable, enough, in my opinion to make them want to register to access more. Once they're signed up, again, just enough to encourage participation.
Be kind, I set the board up 3 months ago and we're progressively growing, steady and controlled.
Any and all input, comments, etc are welcomed!