The Supreme Court has struck down a portion of the Defense of Marriage Act, which prohibited the federal government from recognizing same-sex marriages performed in the states. The vote was 5-4 and the case is United States v. Windsor.
"The federal statute is invalid," wrote Anthony Kennedy in his majority opinion, "for no legitimate purpose overcomes the purpose and effect to disparage and to injure those whom the State, by its marriage laws, sought to protect in personhood and dignity." He was joined by the four liberal justices (Ginsburg, Kagan, Sotomayor, Breyer).
John Roberts dissented, arguing the Supreme Court didn't have jurisdiction to hear the case: "The Court does not have before it, and the logic of its opinion does not decide, the distinct question whether the States... may continue to utilize the traditional definition of marriage."
Very broadly speaking, this means that federal marriage benefits can now be extended to gay couples who are legally married in their states. The ruling does not, however, establish a constitutional right to same-sex marriage.
On a micro level, the case itself means that Edia Windsor now gets a refund for the $363,053 in estate taxes she paid the IRS after her wife died (because she now qualifies for a federal tax exemption for surviving spouses).