OK
I have done some more tests the results are interesting
I have tested with Nikon D3S, D7000, D70 & Fuji SLR14n
Overall at anything up to 50 feet, on all cameras, with any lenses, the sharpest AF results are always when I use AF assist on a SB800 or 900 flashgun, with either the flash tuned on or off. It seems that whatever the SB800 / 900 does with its focus assist light, it is very accurate, especially when used with a newer AFS type lens
The "straightforward in the hand , no fancypants settings - gut feeling A/B comparison" of AF performance ... The D3s is by far the best in the pack, the older Kodak FF is also very good, but slow, but the results are skewed slightly by a lack of AA filter. The D7000 and D70 were similar, the 7000, being a touch quicker than the 70, its a hard thing to judge, as one is a much higher resolution camera
Next up I looked at the cameras with tracking. The tracking works OK with the modern AFS lenses. It is non existant or appalling on slightly older lenses. The moment the subject moves quickly, the tracking falls over and then the camera chooses another focus point, no mater what set of settings you use. It would probably be OK for a crawling baby, but not at tracking a kicked football. The Tracking is a lot better on the D3s compared to the D7000. I don't feel I tested the D3s to its 3d tracking capability, I will revisit that on another day. The D7000 tracking just falls over too fast to be useful, however I could have spent another hour revisiting al of the settings and options. I reserve judgement on this
The D7000 AFA AUTO mode with a AFS lens does a reasonably good job at focusing on a human face
All the camera's let me focus on a single pencil in a pot of pencils & pens, at F1.4 using Af-s and then recompose to any corner, and still be in focus (just about). You have to appreciate that the issue is probably me moving a MM or so rather than the focus. What is apparent that this is quite LENS dependant. On a older wide-angle lens, the results were not very good at all. The difficulty with doing this is that we are also throwing into the ring the edge performance of a lens too
All the camera's let me focus on a single pencil in a pot of pencils & pens, at F1.4 using Af-c and but when recompose to any corner the shot fell over (obviously?)
The issue with the cameras with multiple focus points is the points don't go out to the corners, so the moment I tracked a object outside of these points, the camera then focused on something else. The same issue applies if you manually move a point all the way to say the bottom left - the bottom left of the AF system DOES NOT extend to the bottom left of the frame
AF-c on new lenses seems too skittish, and constantly was hunting for different things to focus on. AF-c on older lenses actually behaved a bit more like we would expect. There is a a balance to be had between how fast a lens can focus, and how fast the camera can process, that's interesting
Overall, if I use the shutter release button or the back focus button the results are the same, however for a slower shot, using the rear focus button and another button assigned to exposure gave me the least amount of bad shots. The issue for me is slightly practical, if I am crawling around on the floor, shooting at a weird angle, trying to half hold the exposure button in the cold,I manage to press it whilst recomposing
Now here is the best bit
The very sharpest shots, recomposed out to the corners were when I used central focus point, recomposed, and slightly tweaked the focus manually. However, the hit rate on these was about 4 in 10 for a dead sharp focus. Without tweaking 6 out of 10 were very good. I feel this is more to do with me moving than a camera issue. I will try it on a tripod at some point
What's kind of evident here is that between all of the cameras, the basic - use a single focus point & recompose gives very good results. If you want tracking and the like, the D3s is the daddy, but the options for it are very complex, and don't really suit a photographer who jumps from one type of shot to another all day (like I do)
What has dawned on me is that the U1 U2 modes on say the D7000 are very useful if you have a couple of fave set-ups, and that's your short-cut to getting the camera set up for a shot ASAP. Personally, I hate battling with a whole bunch of settings in real time to get a shot
Footnote
If you are needing to use the AF assist light, or the SB800/900 assist light, they are pretty one dimensional - they point forwards, that's it. In these scenario's I reckon you must always focus and recompose. While I haven't tested it, you are not going to be tracking stuff when the AF assist light or the flash AF assist is being used
) so if your DOF is 10mm at the focus point in the centre, the the edges of the frame are going to be out of focus. This is the inherent danger of focus recompose, twisting the camera to a spot on that wall that was previously at the edge of the frame, it is going to be further away. 
