The first group of people I "came out" to was my current pagan group on campus. Nobody in it is poly but me, but apparently a few former students were. My experience was really supportive. Everyone handled it gracefully and understood that I'm not comfortable telling people about my identity. A few people said they didn't understand polyamory, but I still feel accepted as part of the group.
My experience as a UU Pagan, on the other hand, has been a little mixed. I think it mostly gets mixed/heated when (in a private conversation) talking about polyamory while discussing marriage equality at all. But a few people in my UU Pagan group are very accepting.
I've heard horror stories, however, about UUs at my church being dramatic about poly couples. It's one of the big reasons why I don't talk about it or come out at my UU church.