Recently I read an article that said when using an EF-S lens on a crop bodied camera (Rebel series, 40/50D, 7D, etc) that the 1.6x crop factor still applied. For some reason I didn't think it applied as the EF-S lenses were designed specifically for the crop bodied cameras. I had thought the EF-S 10-22 lens was just that, 10mm on the widest setting and 22mm fully zoomed. Turns out this lens is really 16mm at the widest setting and 35mm fully zoomed. We currently own 3 EF-S lenses so their true focal range breaks down as follows:
EF-S 17-85 is 27.2mm at widest setting and 136mm fully zoomed.
EF-S 18-200 is 28.8mm at widest setting and 320mm fully zoomed.
EF-S 55-250 is 88mm at widest setting and 400mm fully zoomed. (No wonder I like this lens)
So there you have it -- just one more thing to keep in mind when lens shopping.