As I understand it, the active poster count has dropped in the past year over on the WotC/Gleemax boards (starting around the time they brought out the perpetually in alpha Gleemax). For around 9 months or so the word has been "in X months it'll all turn around, you'll see!". To be honest though, it's getting worse and it's a barren wasteland now compared to two years ago. I suspect that it might be a lot of folks have a similar feeling about the place as I do.
My own posting has seriously declined for multiple reasons: general 4e apathy, a number of other regulars dropping off in activity or going to other boards, and the general vibe that community management over there exudes (the complaint thread against Gamer_Zero the "community liason" has reached -80- pages long, and has gone up by like 20 pages in 24 hours after the latest PR nightmare over there in terms of royally cheesing off the community).