My family situation was a little odd. The older kids were brought up very Catholic (I'm #8 of 9), but by the time us youngest kids rolled around my mom was an apostate Catholic. So we said "grace" every night before dinner, though it was never explained why we were saying it. My church exposure was mostly limited to weddings and funerals so I was spared the indoctrination many kids are subjected to.
My high school best friend and I laugh at her first experience having dinner with my family. My siblings and I said the grace prayer so fast it was completely unintelligible and freaked her out. She probably thought we were speaking in tongues.
Nowadays I "come out" if someone makes the assumption that I'm christian (which is almost always here in MN). I don't hide it, but I also don't make a big deal of it. As far as I can tell that seems to be a good tactic. From the reactions I get it seems like not believing is an option that has never occurred to many people. When they find out I'm an unbeliever, and a nice and ethical person I can sometimes see the cogs in their brains start to spin.