I'll pipe up and say that I'd never seen a forum that worked before I was exposed to the Omaha Underworld game.
In the 8-odd years that I've been a LARP-er, it's always been email lists for me. Some of those worked better than others, with some of the clan lists getting six or seven messages in a day, and some of the others getting maybe one or two every couple of weeks, but we weren't given an alternative. Ever.
The other thing is that many of the people in this group are what I would call "hardcore" LARP-ers - people who think that downtime is for getting together with other people and actually gathering IC. They're fans of calling players up, and when they answer the phone, asking if their character is home. There's nothing wrong with that, mind you, but it's not a demographic that would look at a forum setup and say "Woohoo! Now we can interact more!".
As far as fixing it goes, I have no idea. I don't know how to communicate to people that the forums should be seeing more traffic, since it feels like a grand total of three people are currently watching the email list, making it a fabulously inefficient way to get in touch with players in the first place. Maybe we'll get some opinions rolling here that'll help with that. One can always hope!