I signed up in an attempt to redress the balance by recommending this lens as I feel the last few posts unfairly compare it to the Canon L series costing much more. Having used it on my 20D for the past year or so I think it gives good images.
I tested it on my Benbo by shooting targets at 10ft and 50ft using all the apertures at 28mm, 70mm and 135mm. I'll start with the 135mm results as I found mine gave a high contrast and sharp image at its maximum aperture of f5.6 which is always preferable for maintaining a high shutter speed. Stopping the lens down softened the images especially at the closer distance. At both 28mm and 70mm most apertures gave good results (f8 was best) until f13 where it went off. The macro setting is very usable and gives sharp well focused images.
Now a warning... when using on a tripod I found it best to turn the Image Stabiliser OFF as you'll see a softening of the image with it on. For the money you get an above average optic with an Image Stabiliser that works well for subjects without movement. It will NOT allow you to freeze movement in the same way a higher shutter speed will. You can't point it at kids and expect blur free images at 1/30th of a second and it seems from these reviews that some folk thought it would. The same applies to trees in a Landscape, as the effects of the wind will show. It will however allow you to use speeds of 3 stops less if your subject has no movement, otherwise I adjust my iso enabling higher speeds as the 20D copes well with that.
If you can't justify the price of the new EF 24-105mm L Series that's just about to launch, this lens will cover a lot of your photographic needs.