... Action in the bush happens fast...
That's what ... oh, nevermind...
I'm surprised no-one has mentioned the 400 DO IS II, you can be sure that's going to be the premium wildlife lens for many, many people.
I'm guessing he makes use of the zoom and the built in tc. He's got a 200-560mm lens in one package. When that lens came out some guy was gushing about how great it is to be able to switch things up so quickly, claimed it was better than having a set of primes (and yeah, 200, 300, 400 + tc is a lot carry around).
That said, I agree with you on the 400mm DO, I have the mark I version and while it is a little less contrasty than some lenses, it's a great lens, I love it. So darn light for what it is - it's the size and weight of my 200mm f2. I can literally hand hold it with one hand (why I would want to I can't say but it's possible).
I'll be taking a hard look at the mark II, if it is significantly better I'll make the jump, that's a great lens. I'd love a 500mm f4 DO.
Canon has released a few 600mm DO patents, including this one for a 600mm f/4 DO. That's what I'd like to get, though I may bite the bullet and get either the 400mm f/4 DO or the 500mm f/4L II next Spring.