I decided to put my 6950 to mining but I bumped into a problem.
Everything works ok with the miner started (guiminer->poclbm), but when I try to watch a movie (xvid,h264,etc) my screen will freeze and I will lose all mouse / keyboard control (ps2 keyboard, usb mouse) but the music will continue to work in the background until I do a hard shutdown/reboot. Had the same problem with trying to watch a youtube movie until I disabled HW accel.
Since I moved from an nvidia card, I decided it's from some resident driver left around so I went with a full W7 ultimate x64 install. I still have the same problem.
Full system specs : Asus P8p67 pro, i5-2500k, 4gb ram, Asus 6950 direct CU II. Temps are all under 80.