The probability that a god exists is completely subjective. Everyone has their own idea of what the probability of a god is. I referred to this as our "Agnostic Factor" in an older thread called "Math Unites Atheists and Believers". Of course, random occurences are going to affect our personal probability of god. As Mr.Sklansky has said, proof of humans as the only intelligent life in the universe would affect his personal probability for a god.
For the guy who said that the probability of a god is either 1 or 0. Do you understand what a probability is? With no evidence to prove or disprove god, the probability of a god has to be between 0 and 1, but never 1 or 0. Because nobody can say with 100% certainty that there is or isn't a god. If I hit my flush draw on the river, should I have said that it was 100% before it happened?