Conclusion: I bought this when I bought my 50D last spring. I travel and need a good travel lens. What I found is that this lens focusing capability was sluggish, especially in low light/flash and when at a greater focal distance. It struggles to focus in these conditions. There is a distortion around the edges that I don't like either. So...since I have my first big job coming up, I am going to trade up to a nicer lens ( or two).
Pros: inexpensive, lightweight
Cons: soft focusing, autofocus doesn't function well in low-light, auto-focus sluggish at telephoto end, doesn't have distance measure on body
Conclusion: I've been shooting digital as an amateur for 15 years. Stepping into the Canon world I bought a 60D with this kit lens. I thought I would like the reach plus wide angle. I got this but I am very disappointed with the quality of the pictures. Color saturation is only OK, there's no snap to the results. I have reset the camera in different ways to increase saturation, changed other settings, etc, but still disappointed. Compared to the 18-55 kit lens this one falters.
Conclusion: Bought with my 60D at recommendation of authorized Canon Dealer store salesman as "great kit lens". Great perhaps as 18-135 is good theoretical range. Don't care for lens as image quality seems poor, too slow to use indoors without flash, find autofocus slow and noisy and basically feels cheaply made.
Conclusion: I've had this lens for 3 months and all images produced using this lens was not good at all. autofocus performance is not so good, produces a lot ghosting, CA, and vignietting. loose front element. zoom ring was smooth enough but focus ring was too light. contrast and color representation is so bad.
Conclusion: I have used Canon glass for over 30 years having owned most Canon lenses from 20mm to a 300 f4 lens. They have all performed very well and were consistently razor sharp. By comparison, this lens is a disappointment. Not throwing it in the trash wishing I'd never seen it before unhappy but just not overwhelmed; maybe underwhelmed. It has barrel distortion and chromatic distortion on the edges of the image at 18mm.
Conclusion: The only reason I have this lens is because it came with my EOS 60D. There is a plethora of zoom lenses that are 10x more functional and all-around better than this lens. That being said, there's nothing wrong with this lens for someone as an introduction to photography. This would make a stellar lens for someone who is taking more pictures for fun. The lens is very sensitive, and the slightest pressure will rotate the zoom.
Summary: I think this lens is OK as a general purpose travel lens, and, granted, I'm still going through the learning curve with it and my new Canon 60D. Optics seem OK when exposure is correct (thank God for auto-exposure bracketing). Two major annoyances will be discussed in pros/cons.
Pros: Convenient zoom range for all-purpose travel lens. Optics seem very good in some situations, erratic in others. Will hopefully improve with familiarity.
Cons: 1. It's SLOW. Widest aperture is 3.5, and definitely not suitable for indoor sports unless you ramp up the ISO toward the max. And as I come from the film era, I'm hesitant to do that. Also, minimum aperture is, apparently, only 5.6, so not sure about clarity at extreme telephotos. So far my distance photos aren't impressive., 2. Lack of a distance scale. Unless I'm missing something, this makes it very difficult to pre-focus, especially in dim light or lack-of-contra...
Conclusion: It is a nice, general purpose lens. BUT, when I added a polarizer (yes, I removed the haze filter first) there was noticeable vignetting in the corners, so much so that I had to remove the polarizer. I would also be nice if Canon would update the T1i for correction of this lens.