I recently purchased the 17-55 2.8 for my 7D. The focus seemed a bit off, so I took it in for calibration. Since the 7D was outside of warranty, they would calibrate it to a generic 7D for free, but to have it calibrated to my 7D would cost $180. I had them work on the lens only, but I still need to fiddle with MA, so I can't say it was particularly helpful. Calibration is more expensive that I thought, though I just might need to suck it up and give them their pound of flesh.