I've noticed most forums I visit are a bit slow any more. Not slow speed wise, but slow posting wise. That is, unless they have a political section, those seem to be popular now with the presedentials coming up, but I avoid those.
Since Facebook has gained so much popularity it seems that most forums have lost popularity. It's a one stop shop for most people. If you can find the right groups and what not to belong too. Most people I know rarely even get on a computer anymore, and with a smartphone it's just easier to hit the one stop shop for everything.
I prefer the layout of message board forums to Facebook. It's a personal preference.
This is just my theory as to why things on message boards aren't as busy anymore.