I'm using this lens with a 20D. The image quality is great, colors are vibrant and even on a crop frame, I find the 17mm wide enough for most purposes although I occasionally find that 40mm isn't long enough.
If you've just got yourself a 20/30/350D, make sure that this is the first lens that you treat yourself to. You won't be disapointed. This is the lens to go with these cameras, no doubt about it. Additionally, you're buying in to the EF L-Series legacy which famously holds its resale value.
A 17-40mm f4 paired with a 70-200mm f4 would be the perfect combination for a seriously competitive low-cost package. Maybe throw in a 50mm 1.8f for some low-light prime work.
One happy customer.