I wanted to bump this thread and see if anyone else had some news with it. I have had this exact same problem and tracked it down at one point to be the CCC.exe app and something that has to do with it. In that, I thought that it would be addressed in the most recent versions.
I can go days at a time without anything at all ever being an issue. I have also gone as far as to change a registry entry that keeps the machine from purposefully locking when the driver fails, but instead try to recover. From what I can see, it is all driver and software package, no problem with the hardware. Also, for whatever reason, it seems to get worse if I OC it (why the hell would I not with an OC card...)
I had held out that it might be something that ATI/AMD knows about, but if they do, they haven't addressed it at all.