Yes, I had one lockup since upgrading to firmware 1.0.5...was shooting some tennis using the 20D with 135/2 L. Camera was working fine then all of a sudden the shutter wouldn't release. I was shooting in AV and I could change the settings on the LCD but the shutter wouldn't fire. Shut down the camera, popped out the battery and put it back in and everything was fine for the rest of the day. Was using a Sandisk Ultra II 1GB card. It wasn't a real hassle to pop the battery out, but hopefully Canon can resolve this once an for all.