Well, I had another lockup last night. This time I had a 550EX Speedlight on the body and the lockup was somewhat different. There was no image on the LCD, pressing the shutter release did nothing and all controls were unresponsive. I was writing RAW to the SanDisk Extreme 16GB 60MB/S CF card and JPEG to the same 8GB Kingston SD4 4MB/S SD card. I left the SD card in because I wanted to duplicate the error if I could. I ordered and should receive a new SD card soon, a SanDisk Extreme Pro 16 GB Card 95MB/s (overkill I know, I read the camera's SD slot can't write that fast) I'll swap that in and see if the issue occurs again.
On a related issue, for the first time I'm disappointed with Canon for one of there policies. It seems that I can't return my $3,000 camera that is only 3 days old. Canon's policy for store return is 30 days OR 200 shutter releases (I now have 475 releases). Now it has to go for warranty repair. I have to give up my 3 day old camera for 7-10 day repair turnaround!!!