Well I was looking through the forum, and it seems to be running fine. No extra-long load time or anything.
The only thing I notice that slowed me down a bit were people's avatars and pictures posted within posts.
I have noticed that you have a lot of old content sitting around. I don't know how much that's going to affect anything, but a little pruning may help a little. You may also want to check out this topic:
More often than not, it ends up being a problem with the server being too slow though