Andy,
I've had a 20d since they first came out. The only camera shake problems I've had are self induced (shooting too slow for the lense length.) If the sensor in his camera shakes, something is broken. The sensor doesn't just float around in the camera.
EOS 20d, 2 seconds @ f2.8, ISO 100, Tamron 28-75 XR Di
This images is a 2 second exposure and in the full size pic you can read the house number on the front of the house. This was done on a tripod, no cable release and no mirror lock-up.
If you're friend has issues as described he might be better off to send it to canon for service.
Dan