A friend of mine told me about PC and convinced me to join, so he obviously does know :P
Then I met another member whom I became close friends with. So she also knows

Other than that I haven't told anyone, but it's not a secret. I mean, I'm not purposely keeping it from anyone. I don't communicate with my family, so no telling them. Other friends... well I don't have that many and most (at least irl) don't speak English, so there's no point in telling them about a foreign forum...