Just to add my 2 cents...
Don't know much about sensor production, but from following this discussion, it seems like Nikon is trusting Sony with its soul by sticking Sony-produced APS-C sensors (if such rumor is true) into their camera bodies.
I would have some reservations about having a direct competitor manufacture a core element for your major DSLR lines. Looks like self-fulfilling trouble in the long run.
It would sound less risky to have non-direct competitors (too bad the Nikon-Fujifilm alliance got nowhere) do it for you.
Well, at least Canon makes its own sensors. *shrug*