Boy, that sure does describe me....
How much does it cost to belong to Canon Professional services?
I sent back my 50mm f/1.2L becaues of backfocusing, though I don't know if that can be helped because it focused fine at f/1.2, it just sucked up close when stopped down from f/2.0-f/4.0. I sent it back with my 5D, and they were supposedly going to look at them together...
Do they calibrate them at different apertures as well? They claimed to have made an adjustment to a PC board, but I don't know. I do know it came back with the same behavior.
However, I also just returned a 135mm f/2.0 for an exchange. It had the same problem with two bodies (5D and 30D), both of which worked fine with all of the rest of my lenses.
I told Canon, and they didn't explain the whole tolerances and calibration thing. They said that the pictures looked fine, and that if I wanted more in focus, I should stop down. In each of the pictures, I used the center autofocus point, and focused on the TIP of the screw. I told them that the only one which was REALLY right was at the minimum focusing distance, and then as I moved farther away, it got worse and worse.
These are crops that I sent them. You tell me if I'm the jackass.... [] After reading this, if it wasn't for the money thing, I'd be inclined to order a 1DmkIII and a 5DmkII right now! If it's in focus, the performance wide open is phenomenal.