Yes forums are great sources of content. I think the challenge with that is just getting the search engines to pick up on all that content. Well actually it is getting the forums active. One of the points Dave brings up is very important.

When you look at a site, is it somewhere you would come back to every week? He is also right in the sense that you are not goingt to gain any long term high profit players by flashing a crappy banner at them.

Make it interesting, fresh, and unique content.