To reduce my belief on this subject to a simple paragraph or two, I'll say this (forgive the oversimplifications for readibility's sake):
I believe that "exist" is a concept that only makes sense within the framework of how we experience things. I believe that, regardless of what we *think* we mean when we say it, the concept of "exist" IMPLIES certain conditions that may or may not be the case for another type of being (or Being), despite the fact that we cannot imagine what that "existence" would be like. We cannot even conceive of what it would mean to "exist" outside of space and time. We can use mathematical formulas to demonstrate that something must be there and yet not take up space...or we can try to jam two concepts together and, by the fact that they aren't logically contradictory, say that they are "possible" and could "exist." But when it comes down to it, we can't conceive of it, and it is not really something that we can coherently discuss.
Given what I believe to be true (above), we run into some pretty serious problems with our notion of God. If you accept what I put forward in the first paragraph (in fairness, it's pretty much a paraphrase of Kant), then it makes no sense to talk about God existing "outside of time", or being "omnipresent". So now we run into trouble defining what we mean by "God". If we mean God in the same sense as the heavily Greek-influenced notion of "the sum of all perfections", then I think we are stuck in some heavy contradictions and counter-intuitive notions. If we redefine this to fit our spacio-temporal restrictions (our preconditions for experience), then I'm not sure we're still talking about God in the same sense that the layman means when he thinks of God.
Now here's the most ridiculous part: After saying all of that, I *do* believe that God exists, in some sense of "existence", and in some inexplicable way interacts with us and guides us. I believe that any true search for God's existence will lead us to the abyss, and all the hopelessness and meaninglessness that is implied by it. There is no certainty, no proof, no simple explanation that will allow us to look away from the abyss and be comforted; no real search for Truth will allow such a delusion. There is only the LEAP of faith that comes through looking honestly at the abyss and believing that Something or Someone greater than ourselves understands the meaning of it all, and wants to guide us through it to become what we are capable of being. It is a leap; it is not a step forward onto the solid marble steps of our parents' religion, and not a turning away to find some more palatable place where the chasm converges to let us hop across. It is a leap in the deepest sense of the metaphor, a leap that has no immediate visible hope of reaching a destination, or of the security of landing soldily on the other side. I would never blame or criticize a person who refuses to make the leap - it is the more rational thing to do to stay on the edge when you can't see where you might land. I chose to make the leap, and I am happier for it. But even so, I can't even help to explain why. I can't illuminate the other side for anyone else - it's our own choice to make, noone else's.
Does God exist? I don't know. But my "not knowing" comes from the man who has searched, and reached, and tried to make sense of it all, and simply admits the limits of what he has found. It is not the disinterested child's response to a question he doesn't want to answer. I can't expect everyone to come to the same conclusion, but I hope everyone understands the magnitude of the question.