I only had the Lens for a few Days and granted I am not a pro or anything like that, but I have been taking pictures for a couple of years now and I can say that what seems to be lack of sharpness is due to the lens high quality. In other words is a very demanding lens that would be altered by the smallest disturbances.
If you got this lens you must a) know what you are doing b) have the right tripod c) realistic settings for the picture you are taking.
This as lens is an L lens that is bound to give you the best quality pictures in the world within the range for which it was intended.
Many people say this lens does not need IS, and is true for most of the time, however and option such as the 70-200, with IS would be appreciated by many (not me tough), especially those that want a walk around casual lens.