I bought this for use with my Rebel XT despite some history of compatibility problems between the two. The lens seemed to work just fine with my camera, but I didn't care for the combination at all. The sound of the autofocus was really annoying, I didn't like the softness of the images it produced and I lost some critical shots to "Err 99" messages.
The image stabilization is not nearly as good as Canon's and the lens requires extremely good lighting to turn out good hand-held shots. A faster lens would be much more useful than Sigma's inferior optical stabilization.
After turning out a variety of uniformly soft and quite a lot f blurry images, I've returned the lens in exchange for the Canon EF100-400L. Much better image stabilization makes it worth the extra price--I wish Canon would nix the white body of the "L" lenses though.