My immediate family knows, to one degree or another. My mom knows because of the long talks I've had with her, and she's actually swung around from being a lapsed Catholic/general theist to what seems to be agnosticism. I made it clear to her that she was very welcome to continue believing whatever made her happy, but it seems that some of the points I've brought up got her thinking. Other family members know I don't go to church, and that I'm not a believer - but I've never discussed it in great detail, and they seem OK with it. My close friends all know that I'm a non-theist/secular humanist, and they're cool with it. Even a couple who are Christian don't particularly seem to mind, but in general, they're pretty open minded anyway.
I think I was lucky to be raised in an area that isn't incredibly religious. When I was younger, I was a Christian (Catholic), but I never encountered any strong fundamentalism even back then.