Holty, have hired this lens for a few weeks in the past to cover angling events where my 80-200 can't give enough reach for far bank action.
Firstly, the zoom range is great. You can go from doing headshots at 80mm to shooting far off subjects on 400mm in one fell swoop, which is the beauty of superzooms like this. Build quality is good - this is quite a heavy lens - and it comes with a useful tripod bracket on the lens, which makes it much easier to both handle on a tripod (to spread the weight) and it also comes in handy as a carry handle.
AF is positive on my D2x, although not lightning quick. If you're flitting between subjects that are very near to each other then you'll have no problems with the AF; it's when you want to go from 3m to 100m in an instant - it just won't do it that quick.
Optically it's very good up to 300mm, good at 400mm, although don't think you'll be getting 400mm f/2.8-type quality. I've blown shots up to A3 when shooting at 400mm and they're fine, just not razor sharp like the pros get with their expensive glass.
The VR works very well, although I don't have really extensive first-hand experience with many of the Nikon VR lenses. I was getting good exposures wide open at 400m anyway but the VR just helped me to stop down to say f/6.3 and f/8 without running too much of a risk of horrific camera shake. It's a useful tool but not a total safety net.
It's probably one of the ugliest, most cumbersome looking lenses around (especially when the barrel zooms out to 400mm) and going out on a limb, it's not as good as Canon's 100-400mm equivalent both in terms of optical quality and AF speed.
However, it's a useful lens that when used right and when used without expectations that it'll produce images like you'll get from much more expensive glass, will do the job just fine.
I'll try to dig out some images to show
