One of the problems of starting and running a forum is creating boards and subforums. I've always felt that GMTNation has gone the wrong direction in this regard. In my experience when running a board, you should start small and create forums as you have a need for them.
For example, every board below the GMT360 board has the same sub-forums as the GMT360 board, such as Technical, Engine & Drivetrain, Brakes, etc. In the GMT360 board it makes sense because of the amount of activity. The problem with doing the same in the other boards is that you now have, using the full-size platform as an example, 264 topics spread across 7 subforums. If I'm looking for towing information on a suburban, I come to GMTN and I see only 1 topic. I won't bother reading it or making my own, I'll find a different forum that is more active.
Change it up so that the full-size board is just a single forum, and now the person coming in looking for towing info sees 264 topics in the forum that most closely matches his interest; sure, maybe all 264 aren't about towing, but they're at least about the general vehicle type, so he'd have a reason to stick around and post.
Once the board picks up speed, you start to subdivide so that the higher traffic doesn't make individual posts get lost too quickly.
Anyways, that's my two cents. I've put it in here before and been ignored, so we'll see how far it gets.