A bit off-topic, but a couple of folks mentioned focus calibration, which you can do yourself if you have the right tool and a camera that allows compensation adjustments
I just picked this up:
http://www.bhphotovideo.com/bnh/cont...G&Q=&A=details
I'm mainly shooting with a Nikon D4 and 85mm 1.4g, and wide open, the depth of field is so shallow that any variation in focusing due to camera body / lens production tolerances is noticeable, making the lens-align rig vital for professional users.