We did this in Guild Wars, yeah. I'm sure lots of other games are doing it by now. There were a significant number of Problem Customer PCs that would just crash all the time because of stuff that was obviously a CPU or RAM defect, though I don't know if it was half our crash reports.

What kind of stability test is quick enough to run every time the game starts and good enough to detect real problems?

I believe it was actually an ambient check of things like floating point arithmetic that ran on an ongoing basis, and if it ever failed we popped up an error message.

We already shipped with debug assertions enabled in release builds, so it wouldn't have been unprecedented to do things like validate result bytes after doing big memcpy operations or things like that. Not sure if we did, though.

What was the difference between CPU and video card vendors (if you can talk about that at all)?