It's also worth noting, especially to newcomers of DSLR photography, that this lens on a crop-factor body is equivalent to the field of view of a 38-168mm lens on a full frame camera.

For mine, when I used it on the 40D, it wasn't wide enough at the 24mm end, but since using it on the 5DII, I've found it harder and harder to take off the camera. No wonder that Canon sell this as a (albeit very good) "kit" lens with the 5D Mark II.