As is somewhat visually apparent, those states which have tended to take more liberal policies toward gay marriage have tended also to have larger declines in their divorce rates.
Of all the weak-ass arguments against same-sex marriage, preserving the "sanctity" of heterosexual marriage has always been the worst fucking one (how people I don't know getting married is supposed to affect my own marriage is a mystery that continues to confound). And yay! Now there appears to be data that show just how stupid that argument is! It's important to note though, that, in the end, it really doesn't matter: whatever data are uncovered and however they are presented current laws are unfair and that's the real problem.
(hat tip: Mr M)