I am running 2 BFG 6800GT oc's. I have had the issue with the fan stopping, and it scared the $%^# out of me. Way too much spent on this rig for something silly like a stalled/stopped fan to kill it. I found the problem to be related to overheating. When the new motherboard was installed, I (dumb #%%) placed one of the add in too close to the bottom GPU and as it heated up it auto shut off. Disabling SLI, sending messages that I have a SLI capable machine and should install a second GPU.
I shut down the system for a couple of minutes while I moved the add in to above the top GPU and by the time I was finished & turned it back on the fans restarted. I left the side off just to make sure the fan was rotating, It was. I then put the sides back on the case and kept an eye on the GPU temps for a little while.
Next ran several stres tests, aquamark 3d, 3dmark 01, 03, 05 & 06, Sisandra. All tests completed, and scores were better than previous MB. I am quite sure no one will say I was anything other than lucky. I was. But still, in relation to what everyone here is saying, I have seen the fan shut down and the card quickly disable. My temps are a little high as far as I am concerned. 61c top card, 60 bottom card normal usage. Still quite happy though.