This story has an interesting wrinkle in the question of which marriages count for purposes of federal law. Two men were married by the Cheyenne & Arapaho tribes in Oklahoma. The marriage is apparently permitted by tribal law even though Oklahoma law would not permit it. (Thanks to Chad Flanders for the link.)
The news story suggests that the federal government will recognize this as a “lawful” same-sex marriage for tax purposes, even though it did not take place under state law. That appears to be consistent with the IRS revenue ruling, which applies to “any domestic or foreign jurisdiction having the legal authority to sanction marriages.” (It looks to me like that’s an omission in the IRS press release that announced that revenue ruling. The press release says that marriages “one of the 50 states, the District of Columbia, a U.S. territory, or a foreign country will be covered by the ruling.” But a tribe is not any of those things.)