My astrological 2 cents regarding the seeming shift toward non-monogamy:
Pluto is the planet of death and rebirth, destruction and power and whose purpose is to transform or deconstruct (sometimes destroy) that which is no longer just, valid or serving it's purpose. From 1972 to 1984 Pluto transited the sign of Libra which is the sign of relationships (romantic or otherwise) and of how the self relates to the other. Libra seeks that delicate balance between partnership and autonomy. It is the sign of seeing ourself through others. For those born between 1972 and 1984, whose natal Pluto is in the sign of Libra, a deep and meaningful look at marriage and relationships would be one interpration of this placement in your chart. Transformation of this aspect of society would be catalyzed by Pluto in this sign. So during this transit we saw the rise of the divorce rate and the liberation of women from the kitchen (or other traditional realms)!
Uranus is another outer planet with generational effects. Molly Hall calls it "the provocateur, the bringer of the cosmic wake-up call for both individuals and the collective as a whole". With Uranus in play we must expect the unexpected. It is the planet that rules invention and ingenuity. The great disrupter. Whereas Saturn forces us to be mindful of structures or to work within structures, Uranus would have us throw those structures out the window. This past March, Uranus moved into Aries, where it will spend the next 7 years. Aries is opposite Libra on the wheel and as it's opposite sign it embodies the opposing ideas of Libra: where Libra seeks growth and transformation through relationships Aries is there to go it alone. Where Libra is concerned with the other, Aries is concerned with the self. It is a masculine sign of freedom and autonomy.
Uranus' transit through Aries will activate (at varying times) all those Plutos in Libra!
To my mind, this all dovetails into the shifting ideas of marriage and partnership. I can't speak for global changes but certainly western culture is experiencing a shift. But I do think that all over the globe there are other signs of the shift, polyamory is less in the public eye than gay marriage but gay marriage falls under the same umbrella of challenging tradtional ideas of partnership and we've recently seen many countries declare their support for what was once a cultural taboo.
On a side note, Pluto moved into Capricorn in 2008, where it will challenge the very foundations of our society, power structures and traditions.
More on that from Molly Hall here: http://astrology.about.com/od/plutoi...t/PlutoCap.htm
Just more food for thought...