I bought this lens new in December 2005. I have taken tens of thousands of pictures with it, all hand-held, many with the EF 1.4 TC extender. I use it for sports, wildlife, theater, and concert photography. It is well built. The retractable lens hood is a terrific feature. Although larger, heavier, and more expensive than consumer grade telephoto zooms, I consider it to be light and compact, given the build and image quality. It is certainly quite small and inexpensive compared to the Canon super telephoto L lenses. During the winter of 05-06, I stuffed my 350D with this lens into my jacket and took pictures on the ski slopes all day long without a monopod or tripod. It never felt heavy. The images that I’ve taken with this lens have been sharp, for the most part. The autofocus struggles in low light/low contrast situations. I typically shot one stop down on the 350D to improve my odds of getting a sharp image. On the 30D, I shoot wide open much more often with more consistent results. In most applications, the autofocus is quick and accurate. I can track birds in flight with the extender with the right background (blue sky or water). With a gray sky or foliage background, this is more difficult. The image stabilization works well and is useful for still wildlife shots. The relatively close focus of this lens also makes it useful for near macro work, particularly with the extender. I can become somewhat frustrated by the lack of zoom when using this lens for sports, however, and I find myself using a Canon 70-200mm f/4L with the 1.4 TC (100-280mm) sometimes for sports instead of this lens. However, when it comes to low-light situations such as nighttime football and theater/concerts, I'm grateful to have the f/4 aperture. Overall, I’m pleased with this lens and would recommend it to anyone looking for image quality and performance beyond what consumer glass can offer.