I think that anyone who claims to know for certain, without a doubt, whether there is or isn't a god, is just being arrogant.
Slightly off topic here, given the context of the above, but I wanted to add to the above quote and say that, in the argument of the existence of any omnipotent, omniscient and omnipresent God, the burden of proof is not on the atheist but rather the believer or the God himself.
It is not arrogant, I think, to state that there is no empirical evidence of the existence of any God. If someone were to present evidence to me, I would sit down, consider it, and change my views accordingly, but in the absence of evidence? I think this is being open minded. Show me evidence, and I will believe. Until then, I have to concur with Dawkins' closing lines in his letter to his daughter:
"And, next time somebody tells you that something is true, why not say to them: ‘What kind of evidence is there for that?’ And if they can’t give you a good answer, I hope you’ll think very carefully before you believe a word they say."
As an aside, I like how this thread has become more than its original intention. Nice to have a good debate