I'm an amateur with a Canon Xti. Before I bought this lens to replace my 18-55 kit lens, I did a lot of internet "research" on sites like this one, and I also tried some of the competing lenses such as the Canon 17-85 and 17-55 hands-on. I really wanted to avoid a third-party lens, as many had advised, but this Tamron appeared to be the best value in my judgment. I really wanted constant 2.8 aperture more than I wanted IS (when I take landscape shots, I use a tripod anyway), and I didn't have the $1,000 for the 17-55.
This lens has excellent image quality. Also, it's relatively small and light and it comes complete with a lens hood.
There is visible barrel distortion at the wide end, but the thing that bothers me the most about this lens is that the focusing ring (which is in front of the zoom ring) turns when you use autofocus. Some folks like to cradle a zoom lens in their hands for support. Be careful doing that with this lens.
Overall, I'm very satisfied with this purchase.