It doesn't take a seer to see that the Supreme Court will eventually hold that same-sex marriage is a constitutional right. It won't happen this year, it might happen next year, and the odds get better from there. The interesting question to my mind is how the Court (in other words, how Justice Kennedy) writes that opinion.
One rationale is that these statutes are irrational because they discriminate on the basis of sexual orientation. The Court could also say that distinctions based on sexual orientation should receive heightened scrutiny (and that same-sex marriage prohibitions flunk that test). Or the case could be resolved by saying (as Justice Kennedy suggested during the oral argument of Windsor) that these prohibitions constitute unlawful sex discrimination. (e.g., A man cannot marry a man in some states only because he is a man.)
There is one significant advantage to using sex discrimination as the ground for decision. It might eliminate the need for a sexual orientation amendment to the Civil Rights Act of 1964. Right now a statutory amendment is necessary at the federal level to protect gays and lesbians from employment (and other private) discrimination because the "sex" prong in the Civil Rights Act is read to exclude "sexual orientation." If the Court collapses those categories as a constitutional matter, however, one can easily see how courts could do the same for the statute and expand its scope.
The downside is that a sex discrimination opinion would obscure the nature of the harm and deny gays and lesbians a canonical opinion declaring discrimination against them as a wrong. Maybe we want the Court (and Congress) to state this explicitly. Whether that is worth many more years of no protection for gays and lesbians under the Civil Rights Act of 1964 (if that is the result) is an issue that some attorneys and some of the Justices may soon have to consider.