A new article over on Luminous Landscape will be of interest to all Nikon DSLR owners:

“Nikon uses the autofocus sensing mechanism from their film cameras (except for the D2h), and hasn’t scaled it to the smaller sensor size. The net result is that the autofocus sensors, which on the film cameras are bunched inside the 1/3 lines of the full frame, are stretched towards the edges on the digital bodies. This has two consequences:

1. Autofocus occurs with objects closer to the edge of the frame on a Nikon DSLR than it does with 35mm bodies.

2. The “spread” between autofocus sensors is larger, leaving a gap where autofocus doesn’t occur.”

Website: Luminous Landscape - Focus Sensor Locations on the Nikon DSLRs