I was looking for a lens to upgrade from the kit lens (15-55mm) for my Rebel Xt/350D. It was a tossup between this lens, and the EF-S 17-80. I had struggled with the idea that the 28-135 would be cropped so much on my camera, that I'd have a hard time dealing with the lack of the "wide" that I had gotten used to with the 15-55. (On a crop body, the 28-135mm = 45-216mm).
I was able to try out the EF-S 17-80 at a store. I found the distortion at 17-30 to be very bad. The 80mm zoom was not much better then the 55mm I already have. This coupled with the f4/5.6 was a deal breaker for me. - not to mention, this lens typically cost more then the more common 28-135mm EF lens.
I was able to try (and then later buy!) the EF 28-135mm at the same time. The 28 "wide" on the XT, is fine, frankly, its much like shooting with a prime 50 (except for the obvious f/stop difference). No big deal, added bonus, the 28-135 is a f/3.5 - 5.6 lens. So shooting in low light is ok. The IS helps a lot if the subject is standing still. The USM is fast, and crisp. I love the back ring focus!
I wish this lens came with a hood. It would be 100% ideal for me, but e-bay sourced out a cheap one just fine.
There is some "shake" at the end of the barrel, and there *is* zoom creep. But, for the price I paid, and the fact that the lens takes nice crisp photos, I can live with it. The 15-55 lens is so small, I can toss it in a day bag, and keep it on hand if needed. Its the ideal upgrade lens, for the XT, and frankly is more useful then the EF-s 55-250 lens that is often sold as a "tele" lens for the XT.
At this point the lens spends most of its time on the camera body, and not in the bag!
All and all, a great upgrade that shows how nice of a camera the XT is (was!), and for me the prefect lens to upgrade to!