SCOTUS Blog publisher Tom Goldstein provides a quick analysis that, to sum it up, says it looks unlikely a majority will rule up or down on Proposition 8. Many of the justices think the opponents of gay marriage may not have standing (they aren't representing the State of California, they're just activists). Second, on the constitutionality question, Justice Kennedy seems to be the deciding vote (surprise!). Kennedy believes the jury's still out on the "social science of the effects of same-sex marriage" because it's a new phenomenon, Goldstein writes.

Here's his thinking on how this plays out:

If those features of the oral argument hold up – and I think they will – then the Court’s ruling will take one of two forms. First, a majority (the Chief Justice plus the liberal members of the Court) could decide that the petitioners lack standing. That would vacate the Ninth Circuit’s decision but leave in place the district court decision invalidating Proposition 8. Another case with different petitioners (perhaps a government official who did not want to administer a same-sex marriage) could come to the Supreme Court within two to three years, if the Justices were willing to hear it.

Second, the Court may dismiss the case because of an inability to reach a majority. Justice Kennedy takes that view, and Justice Sotomayor indicated that she might join him. Others on the left may agree. That ruling would leave in place the Ninth Circuit’s decision.