I generally will be open about what I believe in with people I feel or intuit are open to different belief systems, and come from an attitude of genuine curiosity rather than 'I'm right, you're wrong" ego mentality. I've met quite a few people who know magick is real in my life already, so that has been good to not have to hide it with them. My blood relatives know what my beliefs are, and they are generally respectful, even if they think it's delusion.
If someone says to me that he doesn't believe in any of 'that spiritual mumbo jumbo" then I can allow him to think that, and say that I think some of it isn't crap...but won't go too into it with him because he obviously isn't open to hearing about it and will most likely just write me off as a nutcase, which, especially if he's the boss, isn't the smartest move unless I want to leave anyway.
It's not something I feel the need to talk about most of the time, but if the subject comes up with people I'm around at the time, I will participate...again, only if I feel they are respectful to different people believing in different things. There is no point in opening yourself up to ignorant people who think their way is the only one.