A federal district court in Massachusetts recently ruled that the federal law known as 'the Defense of Marriage Act' [enacted by a Republican Congress & signed by President Bill Clinton] is unconstitutional. The law prohibits the recognition of same-sex marriage or any same-sex union that in any way resembles a marriage at the federal level. The judge in the case ruled that such a law interferes with state's rights.
Generally the "state's rights" argument is used by conservatives. It's been used to justify everything from retaining slavery, enforcing segregation to rejecting participation in health care reform legislation. In this instance, of course, many conservatives are up in arms that their pet federal law which establishes anti-homosexual discrimination nation-wide has had a significant set back. It seems they only like the "state's rights" argument when it benefits their agenda. But then, shameless, naked hypocrisy from the conservative movement is nothing new.
If this verdict is appealed, which it most likely will be, it could make it's way to the Supreme Court which could strike down DOMA once and for all, thought that doesn't seem likely considering the current political persuasion of the court.