My thoughts:

The Christians are right, in the sense that we who do not believe in God cannot disprove him. Attempts to disprove God are as futile as attempts to prove him--you just can't verify the existence of a concept as nebulous as God (nor will you change anyone's mind, but that's a different matter).

The "Designer" argument, whereby the world fitting us so perfectly leads directly to the inference that there must be a creator is a silly argument as well; evolution explains it just as nicely, and more simply. Moreover, just because something looks so perfectly fit doesn't mean it needs a creator.

The "complexity of life" argument, wherein our complexity must require a designer breaks down as well. Evolution again explains it. Also, just because something is "designed" doesn't mean it needs a designer. Given enough time, and enough trials, a brand new Lexus could form somewhere in the universe, without any designer other than natural forces. It's unlikely as hell, which is why you don't see it, but not impossible.

Why I don't believe in God:
I see absolutely no reason to. I have no evidence against him, true; I also have no evidence for him. Given this, why should I choose to arbitrary believe in a god? I have no evidence for or against a giant man-eating purple hippopotamus orbiting Alpha Centauri, yet I, for whatever silly reason, tend not to believe in Him. Fact of the matter is, it is infinitely more likely that something does not than is its existence. The only way to get me to believe in something with such odds against it (as everything has) is empiricism, in the loose sense of stuff I can experience and stuff that can be proven from my experience. Yes, that includes atoms.

A sidenote: Even if Yahweh is real, why the fuck should I worship him? I never see this question proposed: given the awful nature of the world and of man, and the fact that [b]I[/i] didn't ask to be here, why the fuck should I worship the dude who brought me here? What has he done for me? Sure, he created me, but like I said... I never asked for it, that was his choice. Sure, he can punish me eternally, but doesn't it seem a little cheap to worship something on fear of punishment?

Which leads me to Pascal's wager... the coward's argument.