I also used to be Christian and like Dan Carroll, I realized that I only did so because I was taught to do so... because it was expected.
I guess in my case, believing in an omnipotent being never made sense to me, either. What really turned me, however, was the belief that those who were not Christian would go do hell. My father is a Buddhist as well as a wonderful father and person. I could not fathom the idea of any loving God condemning my father to Hell because he was not Christian. Never mind the rest of the world who did not believe.