Canon EF-S IS USM 9517A002 17 mm-85 mm F/4.0-5.6 Lens

Pros:
5x zoom
Super-fast Ultrasonic Motor
Image Stabilization
Full-time manual focus ability
Circular aperture
Non-rotating front element
Excellent optical quality

Cons:
Size
Weight
Cost
Macro performance

The added telephoto range (5x zoom ratio, 28-135mm equivalent), super-fast Ultrasonic Motor and Image Stabilization were well worth the cost for me. I am constantly shooting in low light conditions, so Image Stabilization has been a lifesaver.

An important note on Image Stabilization: It will significantly improve your hand-held slow shutter shots (i.e. low light) ONLY if the subject is not moving. It lens can't keep your baby from flailing it's arms, but it can keep the image on the image sensor a little more stable and counteract the hand-shake that even the best photographers have.

The lens is large and heavy compared to the standard 18-55mm kit lens, but I prefer its more substantial feel (most of the time) but it will make you camera bag noticeably more snug. If your Camrea is a tight fit with the stock lens, it will probably not fit your bag with this lens - something worth planning for.

The components are all high quality (metal mount, aspheric elements etc.). This is simply a great general purpose with a broad range of abilities.

The one area in which I miss the stock lens is in macro photography, the stock 18-55mm has a very good close-focusing ability of just .9 feet whereas the 17-85mm is at 1.2 feet, with the higher telephoto focal length of 85mm the framing is virtually the same, but I prefer the 18-55mm for macros, it's just good - especially for the price.

The cost is considerable, especially if you are upgrading for the first time, but there are a few things to consider:
1] For $400 (or less), you can extend your camera body’s usefulness considerably. If you have a $1200 30D, that’s a sound investment.
2] If you are replacing a kit lens, they fetch $70-$100 on eBay.
3] If you think you want something that’s full frame compatible (meaning an EF and not a EF-S) for that “some day”, consider that Canon is still producing APS-C (EF-S) sized cameras by the millions, literally. MEANING the resale market will be quite strong for decades to come.

If you're looking for a good Pro-sumer choice, this is it; if you're looking for a professional Lens with awe-inspiring optics, look at spending a grand (or two) more (USD).

The 17-85mm is one of Canon's better general-purpose lens for crop-factor bodies, offering roughly the same field of view as a 28-135mm on a full-frame camera body. The USM focusing is fast and silent. The image stabilizer gains 1-2 stops of shutter speed below the focal reciprocal. The macro range is not a substitute for a true macro lens, but is better than nothing in a pinch. The zoom is reasonably well damped, although it may try to "telescope" whenever zoomed anywhere beyond 17mm. Build quality could be a little better but it's not too shabby at its pricepoint. And finally, the optics: the lens is slightly soft at its base aperture and zoom of f/4 and 17mm, sharpening up considerably by f/5.6. If cost is no object, the newer 15-85mm gets very high marks for image sharpness across the entire aperture range, and also stops down to f/3.5 at 15mm for improved light gathering, but if you're stuck with the 18-55mm kit lens and have a budget that peaks around $300, this is pretty much the ideal intermediate lens.

I love this lens!!! I have NEVER used or owned any type of camera that had the capablility to accept different lenses. I have always used the instamatics or point and shoot digitals. I love photography and the feel of print pictures. So this review is coming from a COMPLETE amature in every sense of the word. I purchased this particular lens after my husband gave me the Canon Rebel XT for my 40th birthday a few weeks ago. He also booked a trip to China for me and he knows how much I love taking pictures. This lens was the ONLY one that I used for all 1600 photos of my trip and they ALL came out great! During the Peking Opera and Acrabactic shows in a very dark theater I did not use my flash or a tripod ever and every single picture came out crystal clear. I can't say enough about this lens for one thing, I don't know all of the proper photograpic jargon to use. However, this is a nice lens and very light weight. I also like the Macro feature too. I am still playing with it and if a complete novice found pleasure with this little lens I'm sure a more experienced user could really make use of all the bells and whistles featured with this lens. Oh...I almost forgot to mention, I used a polarized UV filter on this lens and the lens cap fits right over it. I read somewhere that you could not use a lens cap and filter together but it worked fine for me. This lens is worth the money and can easily be the ONLY lens that one would use during average photo situations like vacations and family snaps.

Happy IS USM Lens Owner
Barbie

I got this lens a few days ago, so these are first impressions. My comparisons are to the kit lens 18-55 IS that was bundled with the T1i

Range is very flexible - a bit of extra zoom is nice if you don't bring other lenses with you all the time.
Focus is much faster - also allows touch up focus manually while in automatic mode. This is the single biggest advantage over the kit lens

Image optics are similar - pretty good but not great sharpness, CA, etc. You do notice the barrel distortion at the wide end, but it can be corrected (go to he review photozone.de for the numbers)

Overall I am very satisfied and don't think I'll want to go back to shooting a lens without manual-touch-up auto focus.

I went shopping for this lens to use as a primary lens for underwater photography. When doing underwater photography the camera is , of course, enclosed in a housing. The part of the housing which encloses the lens is called a port. The port usually onlt fits a limited, and in this case only one, lens. So you have to plan your purchase and the type of photography you want to do in order to correctly match the equipment. This lens offers moderate wide angle through portrait to moderate telephoto thus increasing the photo opportunities with out trying to change lenses and ports in a wet enviroment.
The lens also has auto focus and image stabilization which really helps to insure a better shot.