"Solid, reliable and sharp."4.0 starson by forkboy
Pros: Relatively light weight. Fast focus. Internal zoom so front doesn't rotate making polarizing filters easy to use. Sharp images at all zoom settings. Image stabilization works as advertised.
Cons: Not as telephoto as one might think. No tripod mount ring. Manual focus ring too narrow.
Summary: I purchased this lens shortly after acquiring my Canon 40D in December 2007. I have been very satisfied with the lens in most every manner. It's not too heavy to work with for hours at a time. The auto-focus is both quick and accurate. The image quality is sharp across the zoom range and the issue of barrel and pincushion distortions only come into play if you are shooting anything with lots of horizontal and/or vertical lines. If you're shooting nature stuff there is no need for concern.
I purchased it for shooting wildlife, but have found that its 70-200mm range (even with the 1.6x conversion factor with my camera) limits it somewhat if you are trying to shoot anything small (think birds, chipmunks, etc.) at ranges beyond 40-50 feet. Well, if you are trying to get great closeups, it becomes an issue.
It is a good lens for shooting events with lots of people - great for getting nice close-ups of folks without having to actually get in their face.