That's a complicated question. I go to services (Jewish) at least a couple times a month, had a very traditional Jewish wedding, but I'm an atheist. What does that count as?
I was raised in a non-religious household. God was never a topic of discussion; it just never seemed particularly relevant to anything. The sum total of my religious education was my dad tossing me a bible (old and new testaments) at 16, saying "you should probably understand what everyone talks about".
When I began dating the woman I'm now married to, she was beginning to get back in touch with Judaism and considering seminary (which she's now in). I began going to services with her, and found the mix of tradition, cultural history, and ritual rewarding. My atheism, however, is very much intact.
I think it helps that I'm a 4th generation atheist (my mother's father's father was a very outspoken atheist). I think most atheists that grew up in religious households feel that they have to expressly separate themselves from the religious institutions that they felt were forced on them form a young age. They also feel lied to and deceived, as if they were told Santa was real until they were 25. I never had this problem, and thus feel reasonably comfortable in my skin even when reciting prayers in a group setting.
What will be more interesting is when I have kids. I have no intention of lying to or misleading them about my non-belief in God, but that's a tough set of nuances for young children to navigate. Saying "We do/don't believe in God" is a much simpler way to view the world than, "Mommy believes in God, Daddy doesn't, but Daddy still likes to go pray on Friday nights."