As long as we can conceive of perfection, we can conceive of God. Our notions of God represent that concept of perfection. So, from that perspective, God exists (as a concept). God is an ideal, the ideal. Every culture has religion. We have (most of us) evolved with some undefined, but definite urge to believe in something greater than ourselves. Our notions of God help us fulfill that spiritual need.
Most Deists believe there is a God, a God who does not interfere in daily life or perform miracles or violate the laws of nature (laws the Deity probably created in the first place). The practical difference between that kind of God and no God at all is no real difference at all. A God who does not intervene or interact with us is no different, no more perceptible nor provable, than a God who does not exist. A difference that makes no difference is no difference, so I don't waste a lot of effort trying to prove the unprovable.
I care whether people believe in God, and I am willing to expend some energy explaining what I believe and why. I care more, however, how you act towards me than I care about your concept of the Deity.
To me the distinction between believing in a Deist God or no God at all is found in our attitudes towards life. I find it convenient to think of God as the source of all things, because if there is an intelligence behind creation, it could very well mean that things have been created and set up so that they can work. If it can work, then by God, I'll figure out a way to make it work. If there is no reason for existence, and it's all just pure chance that things turned out this way, then what is the point? Believing the universe was created based on laws and principles we can eventually understand by a God who set it all up to work is a slightly saner universe than a completely random one.
My concept of God works for me. I hope everyone finds a concept that works for them. As far as atheists and agnostics are concerned, I try to explain it my way. My way doesn't need evidence. It is an attitude thing. I will offer my opinion, but I will not tell them how to think. In return I expect them to have the same respect for my beliefs. If I am deluded, then so what? I like my delusions!
I would rather spend a lifetime hoping for something and being wrong than a lifetime expecting nothing and being right. --Source unknownhttp://reasonandspirit.com/