Over at Mixing Memory, there's a thread where they're discussing the "fundamentalism" of New Atheists such as Dawkins, Harris, and so on.

One interesting point that came up was the charge that someone like Dawkins, who is utterly committed to a naturalistic worldview, would never consider any experience evidence for the existence of god. One commenter asserted that if god revealed himself and started performing miracles right and left, Dawkins would think it was an alien race putting us on, or that he was hallucinating, or that he was in some kind of Star Trek-like holodeck.

First of all, it seems pretty arrogant to claim to know so much about another person's mental states that you think you can predict with any certainty how they would react to extraordinary circumstances like the appearance of angels or god. But I think it's a fairly interesting question nonetheless.

So what would it take to convince me that there was a god? Well, if a booming voice woke everyone in the world up tomorrow morning in some sort of universal language that everyone on the planet could understand and said that he was going to make his presence a little plainer, that would be a start. If he created a few new species, transposed some continents, and altered a few fundamental constants (like the speed of light, ever so slightly), actual miracles that masses of observers could independently record and verify...well, that'd go a long way in making me change my view of the way the universe is organized.

Sorry, but a blurry face on a tortilla ain't gonna do it. And neither are fourth or fifth or 800th-hand stories retranscribed hundreds of times from dozens of ancient, superstitious, semi-literate goat herders.

But a few present-day, global-scale, honest-to-god miracles...that would do the trick.