I think the phenomenon is a lot more simple and obvious than people realize, and they want to harp and bitch and blame it on people they dislike.
Fact is, I believe the fascination of message-boarding has peaked - or at least plateaued - and now theres a lot more places for them to go. A few years ago, I remember being really jazzed when I "found" a place where I might enjoy spending time, making some "friends" in the community. Now I surf more and join less, and comment less.
The world is not the same as it was in 2006. Everyone's webspace was coming online, and now its very common. Back then, it wasn't. Some people were still on dial-up. A few years prior, everyone was on dial-up. So there was a big explosion of people getting on-line, like a wave, from about 2000 to 2005, and then a massive rush of hyper-speed when DSL hit.
That caused every asshole on the planet to freak the fuck out, and now they're more used to it. The big OMFGZ I can bug everyone!! is over. Their maturity has kicked in a little bit. It gave everyone that kid-rush, and I mean everyone. The internet changed the world, and that big splash had a lot of perverse effects. But like everything, people get used to stuff, and it stops being so much fun.
I'll betcha you could go to lots of really big communities, like Fark or even YouTube, and their admins will probly tell you the same thing, reportable offenses are down.
Al Gore can relax, his invention has not ruined the world. We got ourselves under control.