This Sunday's Time brought us the story "Gay Couples, Choosing to Say I Don't," which featured some cute couples with whom I am quite sympathetic. They are all couples of the Times Style Section persuasion, meaning wealthy and well educated. The demographics of gay married people are so in flux that it would be hard to make any substantive arguments, but that probably won't stop people from trying.
It's been clear for a while that among straight marrieds, wealthy and middle-income people get married and low income people do not. I'm not sure that pattern will hold among the newly marrying gays. When they marry, low-income straights may experience a marriage penalty in the form of loss of benefits, without any tangible advantages. In contrast, even low income gays may calculate that the family protections offered through marriage (and for some newly available insurance benefits for gay spouses) outweigh any losses. Those same marriage protections may not seem as pressing to higher income gay couples, who can create legal protections with a good (expensive) lawyer. So for lower-income gay couples marriage is a poor man's lawyer, while for wealthy gays not marrying is a cheap pre-nup.