I think that it has as much to do with how you grew up and your own personality as your intelligence. The way I see it, those that are brought up to be religious usually are; those that break that upbringing are generally the rebellious type anyway. Myself I was raised with an open-door approach.

Basically, my parents were religious but didn't push it on me either way. Some friends started going to sunday school so they asked if I wanted to go. No big deal. It sucked, I left. No big deal. The decision was left up to me.

Anyone I've talked to (not that that's many) that has had any kind of say in their religious views as a child has chosen philosophies over religions. But I wouldn't say that it has to do with intelligence per se. The most devout religous fervor does lie in the most rural areas, however, which would seem to imply that at least /education/ and /diversity/ have a fair say in the matter...