Wow, you decided to cut it back to 4 main uber-categories? Nice.
However, if this forum proves to be a little "out of the way" compared to the BNC Wordpress blog, there are forums that integrate into the blog a little tidier. Namely, they allow the latest comments on the *forums* to show up on the *blog*. There are widgets that plug in the forum comments into the blog home page, so that the latest comments on the forum show up on the home page. That helps some random visitors to see a lively community in action, right from their first visit.
Hi Barry, of course! This whole discussion is based on the wonderful scenario that BNC attracts a professional web designer and, somehow, a few donations to self-host. In which case a professional designer would probably have their own suggestions for integrated blogging and forum software, some of which can be banged into shape to do almost anything!
The one pitfall of proboards that is really bugging me at the moment is that to follow a conversation I have to remember to click bookmark. In most forums I'm in on the net you just contribute a post and you are automatically subscribed! I didn't know you had actually replied here because I didn't remember to click the tiny little 'bookmark' button and didn't receive the email. That could be a major downfall for future conversations and new members experience of this community.