It doesn't really even seem to be the Rp'ers by themselves. It's kinda mix of them and the GM's. I have a close knit group of friends I oft RP with, and it's been hit and miss. Sometimes we REALLY like the project we're on, and keep going. Other times, the RP gets stuck, and we can't find a way out of it. 

I've had the reverse though. Really RP, no motivation, and I wanted to shoot the people who just would not bloody post. That sucks to the point of psychosis.