I've been thinking about this sort of thing a lot lately and I even briefly made an experimental message board that limited the amount of posts the users could make. The idea was that it would slow down the pace of the board and encourage more people to post.

The idea never really took off, almost entirely due to marketing - I have no idea how to promote such a thing.

The site is currently down but if anyone has ideas how to regularly promote it (and maybe keep out jerks who post bad things) I'd love some ideas.