Use the 17-55 on a 50 D recently in daily use as Always plan. Have decided by comparison with cheaper 2.8 lenses for the "original". Reason: High sharpness and resolution even at the edge, and to the no need to stop at 3.5 or 4. The objective met my expectations. Two small drawbacks lead to a half-point deduction, but I can not display. (To date, only get the 4.0 L 70-200mm and the 50mm "Billigteil" full marks from me) Resin-housing -Without Geli-orifice A pity that Canon does not offer EF-S "L" lenses for Crop-Cams.
An update's when I have a few weeks (and a couple of 100 images).