He convincingly shows that not only is there no evidence for the existence of God, but scientific observations actually point to his nonexistence. Life on Earth looks just as it should look if it were not designed, and indeed, the universe looks and operates just as it should if it appeared spontaneously from nothing.
I find a couple things curious about these kinds of arguments--particularly the ones for the nonexistence of God. First, as long as you're using inductive reasoning (and perhaps this is true even for deductive reasoning), you are not going to get a critical mass of people to make any kinds of inferential leaps with you to get to such a conclusion. I've linked to a report about how Americans would sooner vote for a gay president than an atheistic one. (Please do not read any value assessments for or against gays or atheists out of that--I'm merely the messenger.) People are just not ready to accept these kinds of arguments. (By the way, you should check out The Dawkins Delusion for a laugh.)
More importantly, critics of theism consistently and conspicuously avoid the transcendental argument for the existence of God, which posits that science could never purport to disprove God, because the very operation of science presupposes a universal order, a presupposition that certainly cannot be justified from within science or empiricism, as Hume wrote, and ultimately requires a sort of faith that such an order exists. And once you get to that humbling conclusion, I don't see how one could pooh-pooh anyone for deciding to lodge that faith in a God.
(Sorry if that sounds too "religious" for anyone's tastes. I did refrain, you'll notice, from making any unjustified moral propositions, so hopefully I should avoid rebuke.)