Rico had been wondering about that

John Schwartz has an article in The New York Times about the same-sex marriage squabble:

New York’s new law allowing same-sex marriage could bring renewed focus to an embattled federal law that says other states do not have to recognize such unions. The Defense of Marriage Act, known as DOMA, forbids federal recognition of same-sex marriage. But a less prominent part of the law says that no state can be forced to acknowledge a same-sex couple’s marriage from another state.
With New York’s law applying to nineteen million residents, and those from outside the state as well, a surge in same-sex marriages could ensue, with many of the couples migrating to places where those marriages are not recognized. Twenty-nine states have constitutional amendments that define marriage as being between a man and a woman, and twelve have laws that ban recognition of same-sex marriage. Douglas NeJaime, an associate professor at Loyola Law School, said the increased number of married couples moving around the country would force more states to “deal with interstate recognition” and would also have the effect of “putting more pressure on the everyday treatment of same-sex couples by the federal government”.
Opponents of same-sex marriage argue that the Defense of Marriage Act is, therefore, essential to prevent activists from using the judicial system to undercut the law in those states. “If DOMA is not there, the courts will begin the process of redefining marriage” in the states that have already stood against it, said Tony Perkins, the president of the Family Research Council in Washington, a Christian organization that opposes same-sex marriage.
Kelly Shackelford, president of Liberty Institute, a conservative Christian legal advocacy group in Plano, Texas, said the New York law was “a reconfirmation of the very reason why DOMA was passed.”
But many constitutional law experts argue that the Defense of Marriage Act gave states no more powers than they already had. Tobias Barrington Wolff, a professor at the University of Pennsylvania law school, said: “There’s never been a mandatory obligation on the part of one state to recognize a marriage from another state that would violate local public policy.” Even if the act is overturned or repealed, the effect is not likely to force same-sex marriage upon other states, he said.
The Defense of Marriage Act, signed into law by President Bill Clinton, has been under fierce attack in the courts. Last year, a federal judge in Massachusetts declared the law unconstitutional as it applied to same-sex couples for issues like inheritance taxes and federal health and pension benefits. President Obama has expressed his opposition to DOMA, and in February the Justice Department announced that it would not defend it in court, though it would enforce the law until a final court decision was made on its constitutionality.
The power of states to say no is tempered by the requirement of the Constitution that they need to work together, even when laws conflict, said Jennifer Pizer, the legal director of the Williams Institute at the University of California, Los Angeles. “The Constitution says in a general way that we’re one country; states need to play nicely with each other and honor each others’ rules,” she said.
But Professor Wolff and others point to a large body of decisions that shows how the states have the power to reject other states’ rules based on public policy principles. Conflicts in state laws over marriage have emerged in the country for two hundred years, he said, and include issues like the minimum age to marry without parental consent, the right to marry first cousins, and mixed-race marriage. The general principle has been that the state where the couple lives gets to decide whether their marriages are valid on a case-by-case basis. Even Southern states that outlawed mixed-race marriages have recognized many of them when the couple resided elsewhere, for example when the case involved the probate of an estate, said Andrew Koppelman, a constitutional law expert at Northwestern University Law School. A couple passing through a state that does not recognize their marriage will often get recognition if one partner ends up in the hospital so that the other can direct treatment, he said: “It should be safe to travel without having to carry a power of attorney with you wherever you go.” Some states are so hostile to same-sex marriage that it is not certain that they will follow those principles, he said. Mr. Koppelman said courts were unlikely to recognize a marriage where the couple traveled to another state to marry— on a weekend vacation, say— in order to evade their home state’s prohibition of same-sex marriage. The principle that each state governs its own residents is “unattractive to supporters of same-sex marriage, including me”, but it has been the prevailing view, he said.
If the Defense of Marriage Act is overturned, it is unlikely to change the states’ ability to say no to gay and lesbian marriage, but a more sweeping decision by the United States Supreme Court declaring a constitutional right for same-sex couples to marry would. That is the legal theory behind the challenge in California to that state’s same-sex marriage ban. But the first lawsuits regarding same-sex marriage that are likely to reach the Supreme Court challenge the Defense of Marriage Act and its effect on benefits in a more surgically focused way. And Professor NeJaime of Loyola said that even with the court fight over California’s law, the Supreme Court tends to decide cases as narrowly as possible, so “I don’t think we’re headed down that road.”

Rico says he'd always thought that a legal marriage in one state was recognized in all states, so he's confused, as usual...