What is the probability of God?

As a logical continuation of the fascinating dialogue we're having back here regarding creationism and probability, I'm going to throw out a question to the religiously inclined who get such a kick out of calculating the (alleged) improbability of life/evolution/complexity/design/whatever.

What is the mathematical probability of God?

No, I'm not kidding. If you're so keen on running the numbers on the statistical probability of the formation of DNA or stuff like that there, then I want to see you calculate, strictly mathematically, the probability of the existence of an omnipotent, omniscient, Supreme theological deity.

Show your work, including all intermediate results and underlying assumptions, and show how this probability compares favourably with your calculations for the probability of biological evolution. Intermediate steps of the form "And then a miracle occurs here ..." will not be tolerated.

Any comments of the form "Well, that's just silly" will be ridiculed mercilessly, then deleted.