europeforvisitors - 6:09 pm on Dec 20, 2004 (gmt 0)
Forums are just content - no different to any other content. That content will attract SE referrals, it's not just about the regulars.
Depends on the forum, the audience, and the topic. Traditionally, though, advertisers have viewed community content with skepticism. (I can remember when AOL had a nominal CPM of $65 in some of its search categories but maybe half that in forums and something like ten bucks in chat.)