Conclusion: There seems to be a lot of quality control issues with this lens. The main problen i have with this lens is "zoom creep". Its also hard to focus manually. Other than that, the lens is good. I traded the kit lens that came with the camera for this lens, and i'm glad i did. Going by the reviews, it seems like there are a lot of lemons that get by quality control, so its a hit or miss with this lens. I would look elsewhere if i needed a reliable lens.
Conclusion: Excellent lens, when it works. The problem is I can't tell when it's going to work, and when it's not. It's almost moody. I stuck with Canon, and got 2 new lenses to replace it. Keeping it as a possible backup. I would not recommend it, especially at that price.
Cons: Slow auto-focus, Poor build quality, sometimes great sometimes a zero
Conclusion: Took 11, 000 pictures with this lens, then suddenly it had a communications failure with t3i. this is a known defect with this lens -- i.e., the flexible cable inside the lens that does the electronic communication wears out and fails. The lens then stops working completely. The lens was bought in 2012 and failed after 18 months (out of warranty of course). That it failed on a trip to an african country was very disconcerting.
Conclusion: The autofocus failed during a trip at the Everglades, I had to work on manual mode all the time. The repair is a very difficult task and costly. I has the lens for over two years, Canon should stop advertising this lens.
Excerpt: This is a great mid-price, all around lens. I use it on my Canon 60D for both stills and video and it's on my camera 75% of the time (the rest of the time I pretty much only shoot on 50mm prime). Auto focus is impressively fast, the range is spot on for a walk around lens, and it can do most of what you want it to do with some imagination. Feels better constructed, is more consistent, and higher quality than the 18-135 kit lens.
Pros: Consistent Output, Fast / accurate auto-focus
Conclusion: This lens failed when I went to the galapagos. Good thing I had a backup, since having no wide angle would have been a big problem. Came home to find out these lenses are simply bad and wear out. Unreliable autofocus past 18mm means the lens isn't worth much. Buy something else.
Cons: Poor build quality, fails due to design flaw
Summary: The EF-S 17-85mm USM is an excellent lens for regular use and good shooting for amateur photographer. Though the one i bought had the usual issue associated with aperture cable, its still a lens worth its salt.
Conclusion: I have had this lens for 5 years and before I bought it I was hesitant because of some bad reviews. My copy of the lens has been great. I have never had a problem and the pictures are razor sharp. I use it on a Canon 50D and T2i. It also focuses fast.