I have experienced that if I run a fair number of iterations of my kernel while DVBViewer (a media player using EVR custom renderer, not using DXVA) is playing, that the risk for GPU lockup is very high.
It is only the GPU that locks up as I am still able to log in using SSH (cygwin sshd on Vista64/ATI5870).
Is this lockup to be expected? I never experience a lockup with that kernel if I do not run a video.
Normally the lockup occurs after 10-12 iterations, but without video I have run 400 iterations with no ill effect. I guess an iteration takes about 30 milliseconds.