Cheers guys, thats interesting. It explains why there are variances in sharpness, but perhaps not why *everyone* seems to have a sharp copy ;-) It seems this is being touted as an exception to the rule when a) it sounds like its not, a duff one is the exception and b) from what you guys have said it might very well only be sharp on that person's body anyway.

I have to say I find all the second point a bit of a worry. Are we saying that if you have a 70-200 2.8 and say a 5D, 20D, and a 1D MK ii, then you can only calibrate the lens to work 'perfectly' with one of the bodies and its going to be slightly off on the others? Whatever the situation, it sounds like I need to establish if my lens is as sharp as it could be.

Is this post purchase calibration something that everyone does and I've just missed this?