Search the subject of "declining forum posts". It's a problem just about everywhere.
Social network sites have taken a big slice of forum activity.
Content is precious and hard to produce. Those who can produce readable and engaging content start their own blogs and get their own following.
It's no fun to take time to write a post and watch it disappear over the time horizon.
Feedback on individual posts are essential to prevent serious posters from drifting away.
Forums need to use some of the simple techniques that facebook uses. Everything on the internet is subject to evolution.
Facebook will inevitably lose it's hold. There will be a resurgence of discussion boards as various formats merge their tools.
Simon is right where he needs to be.