Fixation have been good to me .... but, as you say they don't sort the focus.
I had a 10D that was well out on focus - Canon UK didn't believe me until they saw identical pictures taken with the same lens on our other 10D ! To be fair though, when they looked at the camera they said it was definitely wrong and adjusted it. After that it was like a new camera .... or to be exact, the same as my other 10D had been out of the box.
So, for camera focus issues I can give Canon UK 10/10 ...... however, lenses are, in my experience, a different matter -
Canon UK had 3 goes at sorting the focus on a 24-70L I had ..... they failed and the lens got replaced, effectively by them. They only accepted it was a duff one after I took images with our other 24-70L which was fine and, like the 10D senario, sent them in as a comparison.
I sent a 70-300 DO back twice for softness / out of focus images compared to other 70-300 DO lenses I had seen and they kept saying it was 'within tolerances' when it was clearly rubbish. I ended up selling the lens.
I hope this helps - for adjusting camera focus Canon UK were fine but for lenses they were not.