The private beta period of the Roleplaying Game site on Stack Exchange is now over. It is now open for everybody to come in, ask questions, and give answers. The reputation system is woven through the site and give great feedback on the quality of the answers and questions. The Stack Exchange faq spells out how it differs from forums and regular Q&A sites. The short answer is that it is no one thing but a bunch of little stuff adding up to a pleasant place where you can go for answers.
I would also add that it works best with experts in the field. So if you are a professional, been playing or refereeing for a while, you might this to be a place where you can share you knowledge without the usual issue involved with forums discussions. and that is more dynamic then writing a blog or article.
Mind you it not going to replace a forum's sense of community as it is highly focused on getting answers to questions not general conversation about a topic. But it works as a nice adjunct.