All forums are generally suffering the same thing I have found.
I am a member of a 4wd forum that used to a number of years ago have more posts than you could watch each day, now you could check in once a week and be all over it all.
I think there are a few factors at play, moderation I think plays a big part and the wider audiences now available on more social networking sites mean forums aren't really as popular.
There are a number of networking sites photo based where you don't need an external host or anything, arguably, if we all 'liked' each other of flickr we wouldn't need to be on the forum at all. A number of those sites also host forums that seem to cater to a wider audience. More muppets, trolls and flaming but hey, its how the kids roll these days.
C&C always welcome