Matthew has a great explanation of why G�del's theorem doesn't apply to the existence of God. But, it does apply to the NON-existence of God, because atheist arguments are always grounded in the assumption that the Universe is a formal system. For a good example of an intellectually consistent atheist argument in this vein, see Den Beste. As a result, the existence of God is an undecidable proposition, so the statement "God doesn't exist" cannot be proved (or disproved). So atheists shouldn't be so sure! Q.E.D. :)
UPDATE: Background on G�del from a layman's perspective.
UPDATE (for Joshua) : Here's teh Yglesias post.
still, I think Pascal's wager is bunk. Islamic thought places great emphasis on niyat (intention), which is clearly violated by Pascal's mercenary judgement. Faith is not a Prisoner's Dilemma.