Desperate on this as well. I upgraded to a GeForce GTS 450 from on-board GeForce 8200 (no QE/CI) had to use Opera for Youtube LOL

Problem in 10.6.8 is my system freezes! I am actually running a QuickTime video on the background just to get a few hours of use. Before I could only use the system a few minutes.

Next thing im going to try (since I don't use it) is disable the HDMI on the board.