I've never been much of a pixel peeper. Today I took some shots at different apertures with this lens. They appeared very sharp when looking at them. Then I zoomed into 100% crops. HOLY COW! The 100% crop looks as sharp as a regular image. I would have absolutely no hesitation printing a 4x6 of a 100% crop from this lens. Realistically, not often that I need that much of a crop from a 85mm on a 1.6 camera, but nice to know that rare option is out there.
I've used this lens before to construct a big stitched image, and no doubt will continue to do so. Amazingly sharp!
Oh, and the focusing. Wow is it fast. With a 40D and this lens it still focuses well except in absolute darkness. I almost feel guilty paying less than $1500 for the combo. It feels like I have pro level AF!