After reading some reviews I expected soft images. Not so. I did tests wide open and was pleasantly surprised with the results. Unless you are doing poster sized prints, this lens works. What was great was the test on the OS. At a focal length of 200mm, I would normally never go below 1/400th of a second, or twice focal length. I shot first at 1/200th and down to 1/100th. I feel I could safely go with a slower shutter speed. This OS thing really works.
My only two complaints are 1: the bokeh, as reported in photozone, was abit unapplealing, but not on all shots...still basically usable; 2: the zoom ring in not smooth. I got used to my 70-200L f4
Overall, the OS with the 18-200 range is just fantastic. Since I got the lens, the other lenses have been in the bag. Oh one more thing, the lens is smaller than i expected which is great with the 400D. Its a great combination.