I've had my D700 for about 8 months now and I continue to be impressed by the capability of this superb camera. My previous camera was a D200, which I still use occasionally.
Most of my photography is landscapes, urban, travel - subjects are generally static or slow moving and I am happy with my autofocus technique in these situations. Where I find that the D700 is very different to the D200 is with moving objects. I think that I understand Dynamic-Area AF with Continuous Servo using 9 or 21 points (a1 and a2 set to Focus Priority) - my results are't always brilliant for moving objects but I get a good proportion of shots in focus (see attached cropped image) and things improve with practice (typically 200-300mm, f8-11, 1/400 or faster, VR on, handheld). I've also tried 51 Points (3D Tracking) with Continuous Servo for moving objects (e.g. neighbour's dog) on a few occasions but have so far found it impossible to use with success. With the shutter button held down halfway and me doing my best to follow the dog with the centre focus point the focus bracket jumps around the viewfinder seemingly randomly between the 51 focus points, on and off and back onto the dog and the resulting photos (CL Release Mode) seem hit and miss in terms of whether the camera has focussed on the dog or the lawn - what have I failed to grasp about this 51 Points 3D Tracking mode?