This is a big topic, and just a short(ish) post thereon. As you know, I'm selectively out. I tend to speak quite openly around friends and am not scared to tell colleagues I'm poly if it comes up. (So far I've told two colleagues - I think the others just think I have a magical boyfriend who can be in several places at once and has a vast number of skills :) )
People have varying reactions. Some people are fine conceptually, then get really edgy when they have to deal with meeting an additional partner. Others ask lots of questions, seem a little uneasy, but manage to treat everyone with respect. You never can really tell. I try to be open to questions and to provide a reasonable amount of info when I introduce the concept. That usually helps.
My favourite thing, though, is this: Both boyfriends and I play a semi-regular role-playing game with a specific group of people. When we started, it was just me and Boyfriend #1. We were invited by a good friend of mine, who's known me for a long time and knows #1 pretty well. When #2 came into my world, and it turned out he loves RPGs, he joined us too.
We met all the other players in the context of the game. They'd seen me be affectionate with #1 on previous occasions. But it's not like we snog during game time. A couple of sessions after #2 joined us, #1 was away. I went to the game evening with #2 and we sat together and sometimes held hands or otherwise behaved in a couply way. Nobody so much as blinked.
Since then one or other of us has had to miss a session now and then, and the other two have generally gone along. Sometimes its me and one of the guys, sometimes the guys and not me. When everyone plays at my house, it's clear that the guys are both staying over.
Nobody has said a word. It's not like they're ignoring it. They just treat it as perfectly normal that I have two boyfriends and we hang out together and all play games together. They've never asked any questions (of me - maybe my old friend got the third degree and I just don't know). This weekend we had a dinner party and I was quite obviously affectionate to both the guys, plus I made a comment at some point about them both being my boyfriends. No blinks. Not a fuck is given by these people that we have an 'unusual' relationship arrangement. And I cannot tell you how very good that feels.
Maybe they're just odd people, maybe it's a nerd thing (yes, we're clearly a pretty nerdy bunch), maybe they're just mature and smart and figure the arrangements are none of their business.
Whatever, it's awesome.