Just in, a federal judge has struck down California's voter-mandated ban on gay marriage, though this first-instance decision is likely to be appealed to higher levels of the American court system. Here's a rather long and confusing story in The New York Times, which does everything except state the above straightforwardly.
I haven't yet read the judgment and can't offer any analysis beyond the tentative paras below (maybe tomorrow).
First, it seems like a good outcome: as long as the state is going to recognise some relationships as "marriages", I don't see any good policy reason not to recognise gay marriages as well as straight marriages. Refusing to do so is a slap in the face for gay men and lesbians.
At the same time, this was a case about the validity of a voter-mandated law overturning ordinary law that provided for gay marriage, which in turn was enacted in accordance with an interpretation of the Californian constitution. In theory, the judgment should be based on fairly technical issues about which law prevails, and it's not clear to me whether the outcome is technically correct, as opposed to welcome from the viewpoint of social policy. Higher courts will doubtless wrestle with that, and I'll try to make sense of it myself when I read the full judgment.
EDIT: See the comments below - apparently the above para is misleading, and the case was decided squarely on issues of compliance with the federal Bill of Rights.
In the longer term, the state should get out of the marriage business altogether and simply leave the courts clear authority to deal with relationship break-ups in an equitable way - looking after the best interests of children, where relevant, and dividing property in a way that recognises the contributions and legitimate expectations of those involved. Courts already do those things all the time, and there's no longer a need for a legal status of marriage in Western societies.
But official recognition of this is a long way off. So long as the state formally recognises some relationships as marriages and assigns them a package of special legal rights, there's no very strong reason not to recognise same-sex marriages. I could make up reasons, and some of them might have some marginal merit, but none of them outweigh the discriminatory message sent by the state if it fails to provide for same-sex marriage.