I have had this lense on my Canon 10d since almost day 1. I had other lenses in the bag and finally decided I was just lugging things around I didn't need anymore. I just supplemented the lense with the 70-200 2.8L IS USM and now I think I have it all covered for me.
I have shot this lense in extremely bright Caribbean sunlight, lowlight, Christmas lights, and flash (you need a real flash to get past the shadow--the onboard won't help you). I do alot of portrait work on the fly, landscapes, and restaurant plates..and I am not disappointed in the range this lense gives me.
It is tough too. This is my walkaround, hike, bike, ski and snowshoe lense and though I treat it well and it isn't scratched, it's only because it's lucky and tough.
If you have to pick one lense to put on a 10d or 20d, this is the one. No question.