Divisions I have noticed first hand;
1) Poly vs. "open", or more specifically, "open to sex outside the primary pair bond", not open to having more than one relationship at a time (secondary or otherwise).
2) Interestingly enough, married folks vs. co-habiting folks. Specifically, some people who are co-habiting have little understanding towards poly folks co-habiting and deciding to marry despite having other relationships.
3) People with children and people who hate/fear children