It was really more of an 'oh, I don't really have reason to believe that either.'
It took a bit longer to realize that being an atheist is pretty awesome.
My Aha! atheist moment was when I realized that no matter what I did, or how hard I tried to make it so, a concept of a loving God was not logical. It was a devestating moment.
I hate going to church (I'm still forced to) and have always been, and I've always had doubts, but trusted my parents that they were right. I DID have an AHA moment, though, after watching Zeitgeist, and even though I now reject a lot of the ideas expressed by it, I still accept that 'God'doesn't exist.