Oh no, I accidentally somehow deleted my previous message. That wasn't my intention. Anyway, in my opinion the D6 AF system is likely to be a significant improvement, with greater customizability and with moderately fast lenses, the cross-type AF sensors cover a larger part of the frame, and there are fewer significant gaps in the sensor array, which should make it easier to work with subjects that change position in the frame, or if one wants to position them in a certain place.
I took a look at the D6 manual and unfortunately with f/5.6 lenses, the area of cross-type coverage has not increased (35 cross-type points, all user selectable, covering approximately the same central area as the D5's 45 points, of which 15 are user selectable on Multi-CAM 20k bodies). But with all my other AF-S lenses, all 105 points are cross type, so full capability is available in that sense.
Dynamic area modes available include 9, 25, 49 and 105 points, single point can be normal or wide, two custom group area settings (C1 and C2) which can be programmed to user's choices of group patterns. The patterns can be modified by pressing and holding AF area selector and multi-selector arrow keys.
