I think that more forums is a nice idea, but it's not necessarily true that more forums == better use. We have a bunch of forums already and there's a lot of overlap in the information posted to the OpenACS forum, the OpenACS 4.0 design forum and the OpenACS 4.0 Testing forum. So much that trying to remember where a certain post was is almost useless.
Since we are building a new site with new forums, perhaps we can use the opportunity to engineer a better way of communicating here. I think Michael's suggestion is best - we should use categories rather than more forums. I don't know how this can be implemented, though.
So with nothing more to add, I'll just shut up now. I need a nap.