I'm only running one at this point (a T20 game), and playing in 3 (doghead's Nameless, and Gomez's CoC and Delta Green games). Now that the Diplomacy game I've been in has ended, I think I can pick up one more, either to GM or to play.
I agree with Gomez's earlier comment that the small party game moves fast, and I think that's the way I'll go with any new games I run. Brown and Andrews are certainly having a blast as a two man team in Arizona (although I am looking forward to meeting us with everyone else, too, Gomez.)
As far as a general drop in activity in the PbP forums, I can't explain it, but I've certainly noticed it. The games I'm running/playing in now have picked up somewhat (quite) recently, but a few others have died out all together.
I think one of the issues for me that tends to limit what I get involved with is that I've pretty much stopped buying RPG material. I don't have a local FtF group, so I haven't been able to justify spending money on things like Eberron, for example, which is the setting most of the currently recruiting games are using.