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Can't Be Beaten in this Price Range (2010-02-24)
I am very pleased with this lens. It is well built; focuses quietly, quickly, and accurately; and is giving me accurate and beautiful color. Image quality has been very good to excellent. Is it is good as my Canon L glass? No, but is is close and a whole lot cheaper.

I love the range (28.8 to 400 on my 50D), so in good weather I leave it on my camera most of the time.

Good purchase (2010-02-14)
I am using a Canon t1i with this lens and i am very happy with picture quality i get. I only shoot in jpeg and image sharpness is enought for my needs. I tested the stabilization at 250 mm and it's works great. For an everyday lens this is a good choice.

good lens overall, as long as you know its limitations (2010-02-13)
I purchased this lens after much research after comparing it to the Nikon 18-200 equivalent. I finally decided on it after seeing the Nikon's prices continuing to shoot upwards and being unable to get a used one off ebay for a reasonable price. I've been using this lens for a week now in various environments and plan to keep the lens.

Overall, I've found this lens to be a good buy- I bought it to replace two lens that covered a shorter range. So far, the images are sharp enough for me, with the caveat that I am not a pixel peeper. I immediately crop and reduce the size of my pics once I get them on my computer. I was worried when I zoomed in on the pics in my camera that they wouldn't be sharp, but they look great on my smallish computer screen, for the most part. The lens feels good in hand and I enjoy the heft, especially since it balances out my D80 with battery pack and external flash. No lens creep yet.

I'd say the most frustrating thing with the camera is the way that it searches when it is focusing at the far zoom range. (UPDATE: I found out that most of the focus issue was because I made an incorrect setting on my camera- its focusing fine now) Colors appear to be appropriate, perhaps a little muted, but when I compared to my 50 mm 1.8, it was about the same, so it was probably a camera setting. There have also been a couple times where it seemed to "lock" up at the far end of the zoom. You have to go to manual and then back in order to get it go back to normal. Annoying, but its only happened 2x so far.

I really enjoy the flexibility of having this kind of range in my camera. I used to fumble around so much with my lenses and now I can just shoot. There was very little distortion that I noticed. Vibration reduction has been really helpful to me and I find myself getting a sorts of shots without my flash that I hadn't been able to get before. According to the reviews its not as good as the Nikon, but its fine for me. Bokeh (that blur in the background) looks plenty good enough for me.

All in all, this lens is all about compromise. It sacrifices a little bit of everything in order to be a lens that you don't have to think too much about. In the end, I'm keeping mine. My feeling on it is, that for 60% of the price of the Nikon, this camera is definitely 85% of the lens, with a little more reach at the end. Highly recommended by this cheapskate photag :).

So far so soft (2010-02-12)
Other reviews are spot on about great build quality, lack of zoom creep, fast auto-focus, built-in flash shadow at wide angle and functional, while said to be less efficient than comptetitor's, optical stabilizer feature. Seem to produce decent macro shots.

I'm one of those who complaints about excessive softness which pretty much makes all the pros less relevant. Perhaps I'm spoiled from using the vastly superior Tamron 28-75mm/f2.8 over last couple of years but the lack of sharpness on my several test shots is somewhat disappointing. I'm using it with the aging Canon 300D body and with this lens it tends to produce underexposed images which are also under-saturated despite the fact that 300D tends to add saturation/sharpness by default to please its intended not very sophisticated user. I understand that the lack of sharpness is a non-issue for 4x6 prints and downsized pictures intended for web-sharing, however you'll clearly see it while looking at a full-screen slide show on a 24" monitor.

I'm fighting the temptation to return the lens thinking I just need to step down (no pun intended) my expectations to reality that other super-zooms are not much better anyways and will present a different set of problems.

Update: after a week of use I came to conclusion that sharpness is adequate for this lens' intended usage. Surely the lens won't win any sharpness contests but overall this lens represent very nice balance of image quality, features, versatility and build at a reasonable price. Still not quite a 5-star for some noticeable off-center softness, but it is a very solid 4. I wish it would let more light in to be more usable for indoor use, but competitors in the same price range aren't better in that respect either.

Maybe not a good match to Pentax... (2010-02-10)
I ordered this lens after I saw the photos my friend took with his Canon XTi. The photos were really nice from the Canon & Sigma combo. However, with my Pentax K2000, images tends to come out blurry even when the OS function on the lens was on. I don't know if it's the built-in shake reduction of Pentax camera is causing conflict with the one in the lens? Or I got a defected lens?

The lens is also heavier than my Tamron 70-300mm because of the built-in motor, thus, hard to hold steady by a petite girl like me...

Another thing is, this lens creates a semi-circular shadow on the bottom of images when shooting with 18mm and camera's built-in flash. Thus, one has to use an external flash when he/she needs to shoot wide angle shots in low light.

Anyhow, I'm considering to return it and order the Tamron 18-250mm instead...