After much reading of others' evaluations here and published test reports, I finally decided to buy the lens hoping I would get a really sharp copy. Well I didn't get a copy that was sharp at short focal lengths. From 24 to 35mm, it is marginal at best. I tested it extensively on newsprint and found that until I got to f8, it was quite soft with my 20D. It is comparable to my 17-40L in the same focal range with the 17-40 being a little better at 35mm at f5.6. From 50mm to 105mm, it performed well in the sharpness testing. For scenics and landscape work using short focal lengeths, I will have to shoot at f8 to f11 when planning to make enlargements over 8 by 10".
In everyday shooting, the lens focusses fast and the IS is better than my older IS lenses. It appears to be well built and, hopefully, it will last a long time as my 'workhorse' lens. I hope when I buy a full frame body, I will still be happy with it.