Bought this lens as a 'standard' prime lens for my Digital Rebel XT. What I found was that it was a fast, sharp, and lightweight lens that made the camera great for long walks. This would be the perfect lens to take to an amusement park, hiking, or biking where size and weight are a concern.
I've also used this lens for macro photography and portraits where it shines. The F2 Bokeh is wonderful and center sharpness is superb even at F2, much better at F4 which is what I use most of the time.
On the negative side, autofocus is noisy. To compare, it's like a drug-crazed wasp trapped in a matchbox. Maybe a mosquito buzzing close to your ear. It's not louder than the shutter, though. If this were a film camera and I was trying to take candid shots, I'd complain more, but it's a 56mm equivelant lens.
Another negative is build quality. They really should make the body of this lens out of thicker plastic. No reason to skimp there as the 'feel' of the lens certainly gives you much more confidence for very little weight penalty. Make it feel solid.
I've got a 52-55mm step-up ring on it as I've got a slew of 55mm filters. This also helps in that the lens cap is further from the body of the lens and easier to remove and replace.
If Canon had made a faster lens in 28mm at the same price point, I would have gone that way. For my tastes, it would have been preferable to have that extra field of view assuming the quality was as good.