I bought this lens new about 16 months ago and have used it extensively for wildlife. It has never let me down and has enabled me to capture pictures I could only dream of before. Anyone interested in this lens is already aware of its large size, weight, and price. I don't consider those negatives, just characteristics of this outstanding lens.
I have only tried this lens on a Nikon D700. I find the lens so well balanced that it is reasonable for me to hand hold it for short periods of time (burst of 50 to 100 shots over several minutes). I typically shoot it on a Gitzo GT5541LS with a fully Wimberley and highly recommend that support package. I did replace the foot with a Wimberley foot and am pleased with the result.
While others have reported better results at f4.5 than f4, I can't tell any difference. With a 1.4x teleconverter, I find that f8 is often better than f5.6. I have noticed a very substantial increase in the need for good long lens technique when shooting with the 1.4x teleconverter.