Upload & Sell: Off
From the day I got my 400 DO several years ago, it immediately became my favorite lens, and, of the various lenses and camera bodies that I own, it is the one piece of equipment that I'm least likely ever to sell. I especially like using it with my 7D. With the 7D and 400 DO, I can put as many pixels on the subject as I can with my 1D Mark IV and 500/4, but, with the DO, I'm using a lens that weighs 1/2 of what the 500 weighs. And, in spite of the opinions expressed by "internet experts" with regard to image quality, when I've presented pictures taken with both the 500 and the 400 DO, whether they be on the internet or with actual prints, to others and asked them to tell me which ones were taken with the 500/4 and which were taken with the 400 DO, I am yet to see a single time when anyone has been able to accurately guess which ones came from which lens.
I think that much of the negative reaction to this lens on the internet was a by-product of the price of the lens. Considering the way that the prices of other Canon long lenses have soared in the last several years, the DO is actually looking, relatively speaking, like a bargain today.