Summary: This was my first super telephoto lense. I have used the 70-200 for a couple of years for indoor sports. This lense is crazy good. Focus is super fast and crips. I needed this lense for outdoor sports and a 2x teleconverter on the 70-200 just wouldn't focus or keep the light right. Now I know why these lenses call for a premium price. You get what you pay for and so far I have shot about 15000 pictures and love it.
Summary: I have used this lens with my D3X for dynamic fashion shoots outdoors where it is very important to freeze a model while she is constantly moving under a directors orders and this lens tracks beautifully giving me tack sharp images, images with a pleasing Bokeh in the background for the client to view immediately on a nearby laptop. Every photo looks like a magazine cover! This is a MONEY lens when you want a telephoto that can perform to the highest expectations.
Summary: The Nikon AF-S VR G 200-400 mm f/4.0 zoom is a pro lens by any means. You may also call it a "tool", so you should buy it if you have a job in mind for it. I bought mine for airplane and airshow photography. I have a Nikon 300 mm f/2.8 prime lens that I use a lot and it is excellent for me under most circumstances, but there are times when a fixed focal length lens is less than optimal. At most airshows the photographer's move relative to the airplanes is limited.
Summary: I regularly shoot my wife's volleyball team in action. It is a hard sport to shoot in available light. By coupling this great lens with my D3 I am getting great results. It is pricy, heavy, but I still love it.
Summary: Having graduated from the 80-400 mm Nikkor to this lens, I can say that the speed of focus and lower apeture over the entire range make it ideal for photographing wildlife. Coupled with a DX SLR such as the D300, it enables the photographer to shoot in low-light conditions. It's worth the added expense.
Summary: I can;t say enough good things about this lens... but there is one thing I wish Nikon had ironed out: Distant Subjects. This lens does not pair well with older cameras like the D2Xs and subject distance is greater than 100 yards. It just falls appart. Images will be either soft or completely OOF.
Summary: This lens is my go to lens for sports. The clarity and detail of images produced far exceeds the bulk and size of the 200-400 lens. It is fast, sharp and easy to shoot with using a monopod. I shoot primarily alpine ski racing during the winter months and in all kinds of weather. This lens was consistently the best gear choice for me.