I think we have a pretty active forum, especially compared to sites of other clubs that actually hold meetings.
I also think we have a pretty good balance of discussion and sales/trading but I think a lot of non-members, or people not attending meetings, only use the forum to buy/sell. Its a practical use of the forum since a lot of members are centrally located, and any site traffic is good in general.
I think the variety of topics discussed is pretty diverse also; different types of fish, different types of tank setups, equipment discussions, etc. Current events pop up, debates on speakers or husbandry tactics, how to set up a fish room, I enjoy that 10 threads might be about 10 different things.
Knowing who you're talking to is also another positive for me, I don't have to guess who's behind the keyboard, and if they they're just parroting something they heard or read somewhere. In the end, as Josh said, the forum is what the members make of it. The marketplace helps keep things active, but if people don't start meaningful conversations, or ask insightful questions, it could get boring.