I'll tell you how the OutFront Forums started and developed because I think most Forums will have to follow a similar path in order to succeed.I started with a simple contact form -- not a bulletin board. I offered to answer questions submitted to the form, and I was as prompt and detailed as possible with my answers. I didn't start with a bulletin board because I felt then (as I do now) that nothing on the Web is a bigger turnoff than a bulletin board that obviously doesn't get much use. My goal was to grow to 3 questions per day and then start a FP disc group bulletin board. I don't believe that the bulletin board would have ever grown to 3 questions per day if I had just thrown it up on day 1. It took several months to grow to the point that a bb was worth doing.
The FP disc group was the best solution for me at the time I implemented it. It's fast and easy, and it works very well for light to mid traffic. It's not perfect. I didn't need perfection at the time.
Eventually, the bb traffic got too heavy for the FP disc group. At that point, it was silly to look for another free alternative. I wanted the best, and I think Infopop is the best. The service is great. The product is great and keeps getting better.