I am running multihead with awesome-wm and the latest xf86-video-ati drivers (not from testing). when i change the power method to profile and change the power profile to low, the screen flashes, my temps start to go down and everything seems normal. a few minutes later the system hard freezes, can't ctrl-alt-del, power button doesn't work on a single press (have to press and hold). i don't have this problem when running dynpm but because i am running dual screens, the temps don't drop at all and hover around 66 degrees.
card is a radeon 6950.
this is a fresh install of arch, had arch installed on the same system about a year ago and didn't have this problem at all.
If I remember correctly this is known to be possible to happen (is that real english? ). In this case, just don't put it to "low", since it's quite experimental.
I'd say, yes. Or use catalyst, which, as we all know, sucks, but its power management is much better.
Or use the medium profile as mentioned in the wiki 
Oh, sorry, yes, R00KIE's right, try medium!