Summary: I bought this lens assuming it would be an upgrade from my EF28-105 and 28-200mm tamron xr. I was wrong, both the ef28-105mm and the 28-200 are sharper at 28mm even when stopped down. Pass on this prime, 5 element construction is not enough, even my cheapo 22-55mm usm is sharper.
Pros: Small, handles flair well
Cons: soft edges, outclassed by ef 28-105mm and ef 22-55mm
Summary: I bought two used copies of this lens in an effort to get a good one. Both copies I tested were very sharp and had good contrast although on one the CA was noticably higher than on the other. On the better copy, images are extremely sharp and CA is almost non-existant.
Summary: Waterfall lovers will appreciate a 28mm lens, and the Canon f/2.8 is no exception. A 24mm lens often puts me into the spray zone. A 35mm lens to me lacks drama. I prefer fixed focal length lenses for waterfalls and similar landscapes to eliminate the ghosting that blemishes photos taken with zoom...
Summary: Great price for this 2.8 lens if you do a lot of architectural work. On a crop factor body (I used it on a 30D and 40D), it produces virtually no distortion. Only gripes are that is focuses slow and noisy.
Summary: I have been happy with this lens so far, using it on a Canon 30D body. The glass is decent quality, without any significant vignetting. It's not particularly wide angle, due in part to the 1.3 magnification factor on the 30D, so not great for getting the full room at a party for instance, but works...
Summary: If you could only carry one lens for your Canon digital SLR, or you wanted to keep your gear to a minimum, this would be the only lens to carry. Of course, you would be limited in your range of photography, i.e. no large groups of people in small spaces; no sports photos.
Summary: Make sure you buy it with the knowledge that you won't be able to use it to the full extent a wide angle lens is used to. Otherwise you will be severely disappointed with this lens. But just how so? I know a photographer that uses this lens for wedding photography with her 10D.
Summary: I bought this lens for a couple of reasons. First of all, I picked it up REALLY cheap used (and you can get it quite cheap even new). Secondly, I really wanted a standard-view lens for my Rebel XT. But honestly, I can't say that I am extremely impressed with it.
Summary: Canon generally makes excellent lenses, but my copy of this lens is awful! Even at f/8 with a fast shutter speed and low ISO, images are blurry when blown up to 100%. It also suffers from severe CA, particularly in bright settings.