I like what I call focused forums. Here are 3 examples:
1. Liz Strauss's The Mic is On nights are focused because they are time bound for an hour or two on one night every few weeks and they are focused because they concentrate on one topic each time (free to wander of course).
2. Amazon's book reviews are another example. The reviews or comments are focused on the book listed. There isn't much conversation between reviews but that doesn't mean there couldn't be.
3. Yahoo Groups can also serve loosely as focused forums. Ask Liz Ryan for example. The members cover a broad range of topics but are united on getting advice from Liz and each other on work and life issues, questions and quandries.
I looked at the DBBB forum but didn't find enough central focus to keep me there at the time.
After my weeks of cogitating I've decided that forums are much like collages...it's a real challenge to take all the disparate contributions and make them valuable as a whole. Focused forums do that successfully much more reliably. And, like any method of building relationships, it takes time and consistency.