Here are a few pics of the lens and 100% Crops taken with the lens mounted on a 7d at F4 to show just how sharp the lens is...
(Taken with Canon 7D, Canon 24-105mm F4L IS USM @24mm F4, 100% Crop)
(Taken with Canon 7D, Canon 24-105mm F4L IS USM @105mm F4, 100% Crop)