Frustrating but somewhat expected, I purchased a 24-70L that turned out to be a bit too soft, especially wide open. I am reasonably confident that my comparison tests were not user error (solid tripod, manual and AF, MLU, etc.). When testing it prior to purchase, I found it to be soft or mis focusing but it was their only model and I wanted to better test under controlled conditions. I expected to buy and return/replace if not satisfied. My tests knowingly pitted it against some tough competition (70-200/f4 IS and my nifty) as well as a lens it should have outperformed (17-85 IS). The 70 was not horrible but not quite right.
I bought it locally so I could easily replace and send out for repairs. The dealer has been very understanding thus far, knowing the issues and potential for this to happen. They ordered two units so I can select the best. They will also return to canon if need be for calibration. I expected this but still wanted this lens for my 5d and 40d.
I used it over thankgiving for family shots. Handling, focal range and speed was great on the 5d. The attached 100%'er shows the focal plane to be aligned with the sweater slightly infront of her eyes (hand held and I think I recomposed). The sweater is relatively sharp but not great, IMO. This is one of the sharpest 2.8 shots taken this day. I am not saying this is horrible, just not as good as it should be. Also, I regognize the 'learning curve' of a fast lens and the DOF is about 4" in this shot. Shutter speed was pretty quick at 1/200 (ISO 800).
I can't wait to get this behind me, get my lens back and enjoy my new toy. I hope I say it was worth it a month from now.