Well, here we are. I have tried, self-conciously, to insert myself in the ongoing debate on the Gnu Atheist blogs, because I think it is a historic intellectual struggle, and so I find it quite tiresome.
Fundamentally, it is obvious what is going on: two different definitions of "truth", one based on the theoretical underpinning of philosophy, and one based on the practical existense of knowledge, vie to be the Truth behind our awareness of Godlessness.
On the empirical side, we have PZ Myers famously stating in apparently unequivocal terms that there can be no evidence of God, not because it is epistemologically impossible (God can fake evidence miraculously to disprove its own existence) but because the more likely explanation for any such evidence does not rely on supernatural entities. To put it squarely, if God Himself appeared and declared himself to PZ, it would be astronomically more likely that brain damage explained it than the existense of God.
I've been a proponent of that position for years, but my claiming it doesn't garner the kind of debate that it does when PZ says it. Lots of atheists, accomodationists, philosophers, and even theists have been discussing what PZ said.
But I understand why those who approach atheism from a philosophical perspective think PZ is being unsophisticated in his philosophy. He is; sophisticated philosophy has gotten an undeserved good reputation. According to sophisticated philosophy, empirical evidence... isn't. There can be no such thing, because ontology can never overcome epistemology. People who have a background in science have learned to conveniently dispense with unwarrented demands for philosophical truth; Karl Popper said almost everything that needs to be said on the matter half a century ago. Empiricism provides only provisional truth, it is true. But other than the claims of philosophers and theists, we have no evidence (or even reason) for the hypothesis that there is any other kind of truth.
This is why I have been, sprinkled all over th einternets, making comments containing what I believe is a basic and well supported fact: we know for a fact that there isn't a God. That isn't a positive claim of knowledge, however. It is a default condition; perhaps in the days before Science, it was reasonable to believe that God not existing is the positive claim. With the success of empricism, however, we long ago passed the point where it is unreasonable to do that. The only reasonable presumption is that the Universe is as it appears: devoid of deities. The claim that there is any or one specific God is the positive claim to knowledge, and it must be accompanied by empirical evidence to support it. Lack of such evidence is (continuing) conclusive proof that that God, and also further proof that any God, does not exist.
I just wanted some place to put this. Further discussion would be appreciated, but I'm not expecting anyone will even see it.