I have the 17-85 which I bought when I picked up my 30D over a year ago. At the time I was making the transition from film (Nikon) to digital and didn't know anything about Canon lenses. The 17-85 really isn't a bad lens and is capable of producing great shots, but the 17-55 is better, but should be, based on the cost. The IQ is very good, but for the cost I don't think the build quality is quite as high as it should be.
I'm going to pass on the 17-55 and get the 24-105 L. I think it has better color and saturation than the 17-55. Even on the 30D, for me, 24mm is wide enough and the longer reach on the other end is very useful. 55mm is just too limiting for me as a walk around lens.
Plus, the way the technology and manufacturing is evolving I really think most serious photographers will eventually end up with a FF camera at some point in the future, as prices will continue to come down. I know I will. No more EF-S lenses for me.