Just. Right off the bat. (AMD fanboy here) What the Fuck is Powerplay?, And dont tell me to fucking google it, I want YOU to tell me what it does. Because i've never heard of it
Media buzzword for a function where the card switches gpu speeds on the fly for idle mode, video-only mode, etc. So it idles at like 150mhz, plays videos at 400mhz, runs games at 800mhz, crap like that.
Problem is that it automatically switches according to load, and some apps may only trigger the switch to high speed modes once they already stuttered for a while... and when running at full speed, one or two game may have some low-complexity scene, that takes less power to render, and so the card switches back to idle mode mid-game, and only switches back after some stuttering again.
This behavior may be optimized per-game though, I've only seen it happen in some emulators which don't exactly get support from the driver team. And in windowed mode too.
However, it's still better than how nvidia cards idle at 60c and burn the fuck down if the cooling fan doesn't run for a moment. And no, Radeons don't burn if the fan gets stopped either. When I was testing my 5850 with a passive Accelero heatsink (no fan), the card hit 130c and then instantly halved its own speed so temps can drop and the thing doesn't melt itself on the spot.
Now, I've been owning Ati cards for a long time now, and I agree that the drivers have several retarded issues. But to say that nvidia has better drivers, that's just nvidia payed fanboy ranting nowadays. And a lot of the issues come out of the fact that the typical gamer has an average of 96 processes going on his PC at the same time.