A hard reboot, with a battery pull if it is a laptop, is the only thing that can get me running again.
I had experienced the “grey screen” plenty of times and in each instance the OS gave up trying to fix the problem and just closed IE. With 7 I have noticed occasionally a grey screen which almost immediately (5 seconds or so)reverts back to normal function as Windows 7 is able to diagnose and fix the problem.
This along with the tremendous increase in speed has made me a fan of W7.