Summary: I bought this lens along with my 30D. I have to say this is a great lens, even compared to 70-200F4 or F2.8. Images are sharp, auto focus is dead on and reliable. IS rocks. I managed to shoot a Chinese evening perform from back seat at ~1/30, ~200-300mm, ISO 800-1600 with acceptable images. IS is really a plus. without IS, at 200 range, you can only in direct sun light, never in doors or at night without a steady tripod. With IS I can handle most of the conditions without worrying blur.

Summary: A major improvment over the non- IS lens....worth the price. I can take action sports shots at full zoom with no blur. Downside...because it is only 4/5.6 aperture you will get some noise on cloudy days and when shooting indoors with poor lighting conditions without a flash.

Summary: Just got this lens and tried it out for 2 days. Very surprised by the image quality this lens can produce. I can shoot at 1/15 sec handheld at 300mm, that's pretty amazing IS performance. Although it's a little soft at 300mm wide open, but stop down to F8, then it's very sharp. Some of the picture can even match to what I got from EF 100mm F/2.8 Macro. The 300mm is extremely helpful when shooting at wild animals, such as birds. Great lens based on the price/performance ratio you can get out of this lens. Will recommend to anyone who needs the long range and in need of IS to reduce the failure rate due to slow shutter speed + shaky hands.