Summary: This is the second "white box" Canon lens I've purchased. It was about half the cost of other places I checked out. I bought it as an "all-around" lens, to replace the EF film 28-200 lens I dropped & broke. I had read that it's kind of heavy, and it is -- but -- it's not a deal-breaker. First use, out of the box, was a small wedding. The pics came out great. It focused quickly. The one gripe I have is the delivery.
Conclusion: I bought this lens in Oct, 2008 to replace the Canon 28-135. I like the longer focal length so I do not have to change lenses. Less chance of getting dust on the sensor. After 5 1/2 yrs of using it, I have had no problems to speak of. Barrel is still very tight, very very few specks of dust in the lens. I and my wife travel extensively and the lens is always used. Auto focus is as fast as with the lens with the USM.
Excerpt: I have used this lens for about 6 months as my walk-around. Images are sharp with good bokeh. Auto focus is quiet and accurate. I use back button focusing which I find is more accurate with my 7d.
Pros: Consistent Output, Fast / accurate auto-focus, Good Walkaround lens, Nice Bokeh
Excerpt: I've had this lens for about a month. I've used it for some landscape, some street pictures around town and some shots of flower gardens and macro photos of flowers. I've used it on a 50D body and a T3i body about equally. I've shot three or four hundred frames with it.<br /><br />Overall, I'd say that it's a pretty mediocre lens. Photozone.de has described it as "substandard".
Pros: Lightweight, Wide Focal Length Range
Cons: Lens Creep, Poor image quality, Poor in Low Light
Excerpt: I owned a 17-85mm lens. There were two upcoming vacations that I wanted a lens with a greater capacity. This was it!! 18-200mm covers everything I could want. The 18-200mm is only slightly heavier; well worth it. The pictures are fantastic. Don't know why I waited so long to purchase it.
Pros: Durable, Easily Interchangeable, Fast / accurate auto-focus, Rugged, Strong Construction