Great next step
One thing I've learned from the reviews here is that it would be easier to weight comments if you knew more about the reviewer. I am still a relative newbie, and have progressed from an old Pentax film SLR, through the basic point and shoot digitals, to a more advanced point and shoot, and about 18 months ago I bought a used Rebel XT from a friend. I thought the kit lens was a huge step up from the p-s cameras, and was amazed by the image quality of this lens. Most of my comparisons are to the Canon 28-135mm f3.5-5.6 IS USM lens, which was the other lens I was considering when I made this purchase. I have had the chance to use both, and am still happy with the choice I made.

The lens makes beautiful photos throughout its zoom range, although it likes natural light better than artificial. It is the best first upgrade I can imagine for anyone who isn't a professional, but then... you aren't really considering this lens if you are. If you do more of your shooting indoors, consider spending the extra $$ for the 28-135 IS USM, which handles low light better. Outdoors I find that this lens works better than the 28-135, producing sharper images especially when you are able to shoot at f7.1 or higher. Images are sharp, colors are true and beautiful, and this lens is capable of some stunning bokeh effects if you take the time to experiment with it. I am able to get sharp images all the way to f4.5 at 105mm, unlike some of the other reviewers here... maybe differences in copies of the lens? I'm not sure why, it just works.

Having said all that, lately I have had the opportunity to spend time shooting with different lenses, borrowing from a friend who is something of a semi-pro, and I am starting to see the weaknesses of this lens. As I mentioned before, it tends to focus slowly in low light situations, and images tend to be underexposed in tungsten light. It can be compensated for once you know about it, but the 28-135 IS is easier to use indoors. If you don't mind using flash it's no big deal, but it's worth mentioning. It's also a little short for my liking lately. I'm finding I prefer to sit outside the action where my presence won't influence the shot, and 105mm is sometimes a little short for that. That's more an issue of suitability rather than a weakness in this lens though.

In summary, this is the lens to get for the first upgrade from the kit lens. It works great as an every day lens, giving up only a little at the wide end compared to the kit lens, but capable of far sharper, brighter images everywhere. For the money you can't beat it. Would I replace it if lost or broken? You bet.

Nice lense for the money
I like the lens, it seems to be a good value. The focal range is pretty good, but I'd like a touch more on the wide end for my 40D as the wide end equates to 44.8MM on the small sensor, but overall I have enjoyed the lens and it has produced good quality results.

What a great Lens
I purchased Canon EF 28-105mm USM II lens a few months ago to go with my Canon XSi. I love taking photos of nature and have captured some really beautiful photos of butterflies, other insects, flowers, and animals with this lens. My pictures have come out sharp, and with excellent color. I appreciate how easy it is to use the manual zoom and the speed of the auto focus is really wonderful. To take close up photos, I just set the camera on the close-up setting, look for my subject, set the zoom, make sure I am 18 inches from the subject, depress the shutter half way and wow - the auto focus is amazing on the subject and the background has just the right amount of blur. The quiet USM motor is nice too so that you don't scare away the insects with a lot of noise. All I have to do is crop my photo - no need for touch up of any kind. This camera and lens go great together.
As far as value, I think the quality is excellent for the money. It is worth every penny.

Excellent for its price
I have owned this lens for about a month now. I opted for this one instead of the 18-55mm kit lens upon reading numerous reviews that it is a great general purpose lens for starters.

I have to say I am impressed with Canon's USM system... and a relatively fast auto focus. I havent had a single time when the subjet was out of focus because of the len's mistake.

It is pretty sharp around f5.6 all through the focal range.. mostly within 28-80mm range.

To sum up:

Pros:
- A good general purpose Canon branded lens. 28-105mm is a decent focal range for starters.
- USM is great.
- AF is good.. mostly accurate.
- Light weight, not bulky in size.
- Decently sharp throughout most of the range.

Cons:
- Colors are not very bright or vibrant.. but a little post processing is all it needs.


Final notes:
The 28-105mm is great for its flexible range and the decent sharpness and USM... I have used it for everything from semi-macros to portraits to landscapes to long exposure shots at night to birds. And the build is professionally solid. Worth the money!!

Great lens!
This is a fabulous lens and the seller was absolutely great about trying to get it to me on time while working with me to figure out the best way. I appreciated their efforts and I ended up with a great product! Thank you!