Hmm, I concur with WhipMagic's conclusions, but almost completely disagree with the reasoning.
From my perspective, I believe the Court will 5/4 (with Kennedy being the swing) provide nationwide same-sex marriage rights. However, I believe the Court will say marriage is a fundamental right for GAY Americans. Marriage is already a fundamental right, and has been for over a century under SCOTUS jurisprudence. Extending it to same sex couples acknowledges the discrimination this insular minority faces, which could, at least in theory, add a "rational basis plus" or "heightened" (a la women/females) scrutiny for ALL laws facially classifying people along lines of sexuality.
On the other hand, if the SCOTUS uses an Equal Protection argument then you're essentially saying a denial of gay marriage is a GENDER issue, which is already a protected class (heightened scrutiny) and would, theoretically, do nothing more for gays other than gay marriage. If the SCOTUS adopts this approach, I predict 7/3 (with Kennedy AND Roberts joining). Roberts will join a case framed as gender discrimination. Roberts will not join a fundamental right to same sex marriage opinion because that has implications for every law that classifies based on sexuality.
I really don't see Kennedy backing away from same-sex marriage, and doing some "but you have to honor other state's unions" argument. It was made in oral arguments, but didn't have much traction or air time.