The lens is very well built, and fairly light. The focus is extremely quiet, and the lens literally focuses in a blink of an eye. The focus and zoom colars are huge and easy to use. The focus colar doesn't rotate while the lens is auto focusing which makes it very easy to hold.
Taken with Canon 70-200 F/4L, F7.1, 200mm, ISO 100
Looking closely at the original file you can actually see the fishing line from the end of the pole to the lure. Not bad considering I was 100+ feet away! I'd have to say the resolving power of this lens exceeds the limitations of the Digital Rebel's sensor. The colors are soo rich! I've never had a picture with this much pop using my consumer lens.
Canon 70-200 f/4L, f/13, 1/200s, 140mm, ISO 400 w. flash
Taken with Canon 70-200 F/4L, F8, 70mm, ISO 100
No detectable Purple fringing or Chromatic Abberrations (red green fringing) even against a white sky. There was no sharpening applied to the above photos other than what was done inside the camera.
Taken with Canon 70-200 F/4L, F4, 200mm, ISO 400
The camera was set to "Sports" mode to achieve predictive auto focus since the subject was walking toward me. It would be impossible to get an infocus picture otherwise. I doubt my consumer lens would focus fast enough to keep up with the apporoaching subject.
In this test, the pattern is photographed at a 45 degree angle. The numbered ticks are scaled at 1.414 centemeters, this coresponds to a distance of 1 cm distance from the lens at 45 degrees.
Purple fringe test:
Canon 70-200 f/4L ($550) VS
Sigma (Quantaray) 70-300 f/4-5.6 ($200)
It's immediatly obvious which is the consumer lens by seeing the suns reflection in the car windows. The lettering on the boat is a blueish black on the consumer lens, and pure black on Canon. The Sigma picture was taken at 300mm, so it may appear sharper than the Canon which was upscaled from 200mm to match image size.