Conclusion: I've had this lens for several years. The images are soft at all apertures. There's a color cast. There's massive vignetting, though PIC removes it pretty well. You'd be better served to save your money for the 17-40 zoom.
Cons: Semi-sharp images, color cast, intense vignetting
Summary: I bought this lens to get a bit wider than The 28-135mm IS which was my first lens for the new 10D. I liked the reasonable size and that I could share the 72mm filters with the 28-135IS. I am not happy with the sharpness of this lens at any f/stop and will not use it at all wide open. I don't know if this is a bad copy or not but since I don't have a warranty to return it to Canon; I will soon E-bay it off.
Pros: Low used price. I like the size and weight. I can share filters with my 28-135mm IS. I like the focal length.
Cons: This lens is not as sharp as I expect from a prime and is not as sharp as the 17-40L that I replaced it with.