It's great to see this topic being discussed, although I am sorry to be joining it so late. IMO, when it comes to dealing with monogamy, our field has relied on conventional thinking without the benefit of supporting research. But there is a growing subculture in America that is not monogamous and will need psychology to be better informed in order to help change policy as well as provide services (for issues unrelated to their monogamous status). There is such a high need for psychologists who are well-informed and unbiased in this area that 2 referral groups have formed to direct folks to therapists who won't pathologize their orientation; KAP (www.bannon.com/%7erace/kap/index.htm) and PFP (www.polychromatic.com/pfp). This growing subculture has developed it's own terminology to describe it's actions: Polyamory=responsible non-monogomy, where all involved know what's going on, with no secrets/cheating; Polyfidelity=folks involved in permanent multipartner (3+) relationships.
It is not suprising that very little hard reseach has been done on non-monogamy, considering the consequences of being "out". Last month MTV showed a documentary about Polygamous and showed a triad of 2 men and a woman, who was also a mother. After the broadcast, the local Children's Services agency took the child away on the grounds of "immorality". With such risks, why should poly folks endanger themselves by being involved in research, even research that could dispute the stigma and pathologizing?
Recommended reading: The Ethical Slut by Easton/Listz (don't let the name throw you; this is a solid book: www.bigrock.com/~greenery/new.shtml) Loving More by Nearing Love Without Limits by Anapol Monogamy by Phillips Three in Love by Foster & Hadady
Websites: www.altsex.org/poly.html
www.bayarea.net/~stef/poly/
www.sexuality.org/l/polyamor/evoltend.html
www.lovemore.com/
www.powerotics.com/powerotics/prof1.htm
www.powerotics.com/powerotics.gener3.htm
www.twomoons.com/ring/index.htm
www.bee.net/cardigan/PAARC/
www.polyamory.com/
www.polyamory.org/sf/essays.html