I heard that 17-85 f/4-5.6 USM IS lens was quite a good kit lens so I decided to test it out for myself.I tested it against the 17-40 f/4L which was slightly more expensive...I mainly tested the lens for distortion, colour rendition and sharpness on its lowest f-stop.
1st test,lens distortion
notice that there is less distortion on the picture on the top(Canon 17-40) compare to the picture on the bottom(Canon 17-85) which have quite obvious distortion.<17mm,f/4,1/30,iso>
2nd test, colour rendition
Notice the red colour on the bottom picture(Canon 17-85) at the top left hand corner is slight softer compare to the picture on the top(Canon 17-40).