I'm a bit confused by the original post. Are you asking whether you should tell people or if we have told people? I'm relatively open about Satanism and am more than willing to discuss the subject with friends/familyif it comes up but it usually only comes up in philosophical/theological discussions - which are kind of rare these days.
As for telling a boss, I can't imagine why your boss would need to know you're a Satanist. I mean, unless you're really trying to stretch and sell the religious aspect of it in order to get the day off for your birthday, citing a 'religious holiday.' ;)
Ultimately it is a private matter that only the individual Satanist can decide upon. Satanism is probably one of the more private religions/philosophies around, so I see why so many people keep it to themselves or release information on a need-to-know basis.
As for telling your boss? If he's religious/ignorant/narrow minded etc. That's it. You did it.
"It's too bad that stupidity isn't painful" A.S.LaVey
My boss doesn't need to know nor does she care what I follow in my personal life. All she cares about is that I am at work, on time. My family doesn't really care either as they have other, more prominent,things to deal with in their lives. My boyfriend is a Satanist so it's just not a big deal all around.
No, but all jokes aside, I am open with my family and friends about it. Other than that, I don't see the need to flaunt my beliefs to the world. Furthermore, the last thing I want to see is people looking at Satanism as some sort of trend, phase and/or something to do.
I think this question should be flipped from “should you” to “why would you”. At least being honest with yourself over the need for a title and the need to advertise it.
As far as my family is concerned, its implied but never confirmed.
As I have always been labeled as a radical atheist because of my youth years, people just don't come to talk to me about religion(see me as "lost"). I am also an horror movie/dark music fan, so when people see any of my satanic paraphernalia, they think it's part of my collections hehehe. So, nobody, except the most informed about the topic, asks me seriously about it. People see it all as one of my eccentricities and just don't care.
At work, I have a personal position to not discuss religion, because of nature of my work.