Well, I post in the trilogy of new boards (mice chat, launching pad, and here). I also have a live journal that I use once in a while. I spend far more time here than on any of the others.
One board that I always like to give props to is the
Straight Dope Message Board. It's a huge board (over 50 thousand members) and has posters from all over the world regularly contributing. The theme is "Fighting Ignorance" and every possible topic you could think of has a thread somewhere. What I like about it is, say someone posts something about a new law. You will immediately get the opinions of a bunch of lawyers. There are experts on every topic there. It really makes for some interesting discussions but can be intimidating. In the "Great Debates" forum which deals with religion, politics, history, philosophy, etc., it is pretty much required that you provide a link to support any fact you are stating. They are pretty hardcore about it. That's why I just read. Anyway, it's worth checking out. I'm "Club 33" over there.