He's on about the "Hickingbotham" review that Gentoo provided the link for. THe 200-400/4afs VR was against the 300/2.8 afs (not the newer VR version though which has a super reputation). From the slides shown, the 200-400 definitely appears sharper at 400 than the 300/2.8 combination with the 1.4 teleconverter at 420mm, which is pretty amazing for a zoom. I think the 300/2.8 is slightly better at 300mm though.
Bjorn Rorslett rates the 200-400/4afs VR zoom very highly, but Thom Hogan is less complimentary about it for some reason. For me personally, I don't think there's enough reach, especially if I'm thinking about moving to a full frame D3 or D700. Guess I'm looking at the monstrous 600/4asf VR!