I enjoyed David Fincher's direction in The Social Network, but I think the main reason why he's likely to win Best Director is because like a lot of actors and directors in the past (Pacino, Scorcese, Jeff Bridges) it's seen as his turn after being ignored so often in the past.

As for Christopher Nolan, I suspect he's like Steven Spielberg, he'll need to direct a very serious film about the Holocaust or something before he gets any Best Director Oscar. Though at least he's not been as robbed as Spielberg was in the 80s (beaten by Warren Beatty? Richard Attenborough?!).