This is always a fun topic! First, I will freely admit that my positive assertion "there is no god" depends upon an act of faith. I can neither prove nor disprove this. All I am aware of is that I have no conclusive evidence (that is satisfactory to me) for the existence of a god.
I also firmly believe that the idea of a 'god' was implanted in my brain by society and my parents. Jgnat asked the very interesting question as to whether or not there is a biological foundation for a belief in the supernatural and I believe there is. Looking back as far back into my life as possible, I never recall a moment where I ascribed the reason behind any experience or event as being due to supernatural forces, in contrast, my sister has always been pre-disposed to a belief in god and this sort of thinking. I think it is only a matter of time before we find a solid genetic basis for the complex trait of a belief in god, or more generally, a tendency to think in supernatural terms.
My career is as a research scientist. I depend upon empirical methods and physical results everyday for my experiments. However, is there an element of faith in this methodology? Absolutely! I have faith that there is some tangible "truth" that I will be able to uncover with my methodology, the difference is, I have no preconceptions as to what that "truth" will turn out to be, once the data is in.
Finally, if I was presented with solid, satisfactory proof for the existence of a god, I can honestly tell you, I would accept it. I am open-minded enough to consider this a possibility.
The question is, to all believers, if you were presented with INCONTROVERTIBLE proof that there was no god, would you similarly accept this?