I never discuss my bipolar at work. But I wouldn't discuss dating, religion, or any number of personal topics there. Fear of Stigma does play a big part, but I am also very private.
My family knows and are supportive. I usually get to know someone as a friend for awhile before I bring it up. I mean I would think it odd if upon meeting someone he or she begin telling me all about some illness they have. If there seems to be a real bond forming, I do it slowly so as it not get hurt. I also try to be matter of fact and keep the drama down. This is part of me and my life. If we are close, you will see these symptoms. Vast majority of the time it goes well. Not everyone needs the same depth of knowledge and intimacy with me. That's ok. The reverse is true as well.