Legal scholar Ed Whelan gives a summary of the two cases pending before the Supreme Court involving marriage, including this summary of the winding path Prop 8 has taken to the highest court:

"...The saga of the anti-Prop. 8 lawsuit would make an unbelievable novel. No federal district judge has ever committed more egregious acts of malfeasance and manifest bias in a case than Vaughn Walker. In the end, Judge Walker concocted a federal constitutional right to same-sex "marriage" and based that right on a set of absurd factual findings. Only after he finished with the case and retired did he disclose that he was in the midst of a long-term same-sex relationship — which means that he had been ruling on his own legal right to marry his same-sex partner.

To compound the farce: The Ninth Circuit ruling on appeal, which also held Prop. 8 to be unconstitutional, was written by notorious liberal activist Stephen Reinhardt. Judge Reinhardt’s wife, Ramona Ripston, directed an American Civil Liberties Union affiliate that filed briefs in support of the Prop. 8 challengers in the same case and publicly rejoiced over Judge Walker’s ruling. Yet Judge Reinhardt somehow refused to disqualify himself from deciding the appeal. Then, in a transparent effort to evade Supreme Court review, he ruled that Prop. 8 was invalid on the narrower (but infirm) ground that it took away a right that the state Supreme Court had previously conferred.

The Supreme Court ought to reverse both the DOMA ruling and the Prop. 8 ruling when it decides these cases at the end of June 2013. Under any sensible interpretation, the Constitution simply does not speak, one way or the other, to the question of same-sex "marriage," but instead leaves the matter to the realm of representative government for decision — to each state to determine its own marriage laws and to Congress to determine what marriage means in provisions of federal law." -- National Catholic Register

James Taranto of the Wall Street Journal throws a bucket of cold water on the notion that Justice Anthony Kennedy is a "sure thing" for gay marriage:

"...Back in 2010, this column made essentially the same prediction [that Kennedy would support gay marriage], and on the same grounds. Now we're not so sure. It seems to us that Kennedy's "powerful, eloquent and compelling" language in these two rulings--as well as Justice Antonin Scalia's language in dissent, equally deserving of those adjectives--makes them seem more sweeping than they actually were, especially the first of the two, Romer v. Evans (1996). 

Romer was the case that struck down Colorado's Amendment 2, a ballot measure amending the state's constitution to bar laws or policies protecting homosexuals from discrimination.

... As it turns out, however, in 1997 a federal appeals court drew precisely that distinction in allowing to stand a law similar in many ways to Amendment 2. The following year the Supreme Court let the lower court's ruling stand, as the Cincinnati Enquirer reported at the time...

... Kennedy may be as activist and results-oriented (on this matter, anyway) as Erwin Chemerinsky thinks. His moralizing rhetoric in Romer and Lawrence certainly has led us to think so. But there's nothing in the legal logic of those cases that makes a constitutional right to same-sex marriage inexorable.