From the New York Times:
Now that Mr. Obama has declared that he believes denying gay people the right to wed is not only unfair and morally wrong but also legally unsupportable, the urgent question is how he will translate his words into action. To start, he should have his solicitor general file a brief in the Proposition 8 case being argued before the Supreme Court in March, saying that California’s voter-approved ban on same-sex marriage is unconstitutional. [snip]
The outcome of the Proposition 8 case is likely to affect the lives of gay, lesbian and bisexual Americans for years to come, even if the final disposition is not sweeping enough to wipe out all state laws currently banning same-sex marriage. A strong filing by the Justice Department, forthrightly declaring that denying the freedom to marry violates the Constitution, would put the full weight of the federal government on the side of justice and could influence the shape of the ruling.