I use it on 1DsII, and it is a damn good lense ! It is small and light but build like an L !
Contrast and colors are just amazing.
Sharpness at f/4 is very good in center, with corners softs.
At f/8, extreme corners (really extreme !!) stay a bit soft, but overall sharpness is just outstanding, it resolve really thin details everywhere ! A bit of distortion but hey, it is 17mm on FF !
I prefered 17-40L to 16-35II due to 77mm filter alone (I don't need f/2.8 at such focal leghts). Definitely a keeper, specially at that price !