Paul's post below perfectly captures the state of play, and as he and Dahlia Lithwick point out, Judge Walker's detailed and shrewdly crafted opinion seems written with Kennedy in mind. And optimism in this case isn't entirely misplaced. Conservatives were skeptical about Kennedy when he was nominated in the place of the defeated Robert Bork in substantial measure because of concerns that he was sympathetic to gay and lesbian rights, and these fears have (thankfully) turned out to be well-founded, as the cases Paul mentions indicate. To provide a little more grounds for optimism, what's striking about Lawrence is not just the holding but Kennedy's willingness to directly repudiate a precedent that was less than 20 years old and was joined by two members of the Lawrence Court ("Bowers was not correct when it was decided, and it is not correct today. It ought not to remain binding precedent"). This is unusual -- Earl Warren was far more gentle with Plessy v. Ferguson in Brown -- and shows that Kennedy is willing to directly go after conservative sacred cows in the right circumstances. One could also mention his very surprising decision at the time to provide the swing vote to uphold Roe v. Wade 1992, when litigators on both sides expected the Court to overrule it.
So why am I skeptical about Kennedy voting to hold Proposition 8 unconstitutional? I think there's two important differences between this case and the previous major liberal opinions written or co-written by Kennedy: the breadth of the case and the level of public opposition. Romer was a very narrow opinion directed at an unusual referendum passed in a single state, and while it permitted states and localities to extend civil rights protections to gays and lesbians, it didn't require them to do so. Lawrence struck down rarely enforced "sodomy" laws in a handful of states, laws that by 2003 as reliable a conservative as Justice Thomas was willing to call "silly" even as he argued for their constitutionality. The plurality opinion in Planned Parenthood v. Casey -- which upheld Roe but gave the states wide latitude to regulate abortion -- was for better or worse consistent with a large majority of public opinion in both respects. A decision requiring all 50 states to recognize same-sex marriages would go beyond any of these cases, both in terms of its immediate social and policy impact and the amount of opposition it would generate.
So while it's possible that Kennedy will provide the swing vote to strike down Proposition 8, I have the uneasy feeling that he'll consider it going too far too soon. But I certainly hope that the optimists are right.