My opinions on marriage are I don't think it's right for married people to be granted (or denied) rights not similarly extended to everyone. So, for example, I don't think there should be tax benefits to marriage at all, as that discriminates against the non-married.
Also I believe culturally-forced marriage is wrong, but if two people wish to be recognized as a married unit, that's fine. Although I do believe most marriage is of the culturally-forced variety or at least for cultural-appeasement reasons.
I think it's perfectly fine to live with someone as a couple without having to get married. It's even fine to have multiple partners provided everyone is fine with this arrangement and there isn't cheating going on. And I think it's also fine to have relationships come and go. Just because you've found what is presently an amazing relationship doesn't mean it necessarily always will be that way, whereas some definitions of marriage enforce this "you're stuck together forever even if you hate it".
So, all of that said, that's about marriage for anyone, straight, gay, or whatever else. I don't think there should be differentiation between straight marriage, gay marriage, or any other kind of marriage. Want to marry your car? Stranger things have happened.
And I believe most of society would be better off if people stopped caring so much what other people do in their sexytime. Ergo, any public benefits of marriage should be nullified, as one should not be seen as "better" or "worse" for being married or not married as the case may be, although frequently in this society there are expectations for marriage and people will look down on you for not being married after a certain age, which is wrong.