My mother knows, me brother knows, and a few of my friends know. My friends that don't know, and most of my family that doesn't know is mostly because it just hasn't come up yet. Some would approve, others not so much, but overall it wouldn't matter and nothing would really change. The only person I'm really concerned about telling is my father. He'd accept it, but not without being a huge pain in the ass.
My dad is the kind of person that has a perception based on the ideal that "there's a way things should be, because that's just simply the way it is." And yes, he's a big fan of Fox News. He's generally fairly tolerant of people that don't fit in this ideal. For example, he doesn't like the idea of homosexuality. However, he doesn't have anything against homosexuals, and he even voted against a gay marriage ban when it came up where he lived at the time. In his mind, it's okay for other people to live their lives as they want, but he doesn't see me as a person. I'm his son, and I should accept his opinions and values as my own without question, simply because "that's the way things should be." He's not actually as controlling as it sounds, he just very judgmental of me, and when I disagree with him, assumes that I'm being naive rather than it being my actual opinion. It's rather annoying.
Polyamory in itself isn't the whole issue. For the most part, that wouldn't be a big deal. It's more about who I'm involved with. Several years ago, I started becoming close with a friend's girlfriend. He was fine with us being friends, but it started getting to a point where I thought it was crossing a line. She said she wanted to leave him for me, and when I wouldn't go along with it, she started telling me lies about how he was physically abusive, and threatened suicide if she ever left him, slowly wearing me down and making me hate him. And, well, I went along with it and started having sex with her behind his back. Of course, I lost my friend over it, and that relationship didn't last long.
My father knows about that situation, and saw it coming before I did. And, of course, told me to stay away from her. I didn't listen because I didn't know I was being manipulated. While my dad knew I was, he didn't explain this to me because of his belief that just telling me to do something should be enough and explaining things to me is beneath him.
Currently, I am involved with the girlfriend of another friend of mine. This time openly and with complete honesty. In fact, he set me up with her. In my father's mind, however, he won't see this situation as being any different from when I did it without consent. Even though my friend set it up, my dad will tell me that it'll still cause tension in our friendship, and in their relationship, and he'll decide for me that it's not worth it, and it'll never work out, blah blah blah.
I'll tell him eventually. I want to give my current arrangement more time to develop. There's a very good chance it'll work out, but there's some difficulty and it's going to take time. I want to make sure it's going to last for a while at least before burdening my father with ideas he's not used to. If my current arrangement doesn't work out, I'll tell him then, because I'm absolutely sure I am polyamorous.