By denying certiorari from U.S. Court of Appeals cases striking down same sex marriage bans in Virginia, Utah, Oklahoma, Indiana and Wisconsin, the U.S. has effectively legalized same sex marriage in those states and also in Colorado, Wyoming, Kansas, West Virginia, North Carolina and South Carolina, which have rulings striking down the ban at the trial court level and are in circuits that have rulings to that effect which are binding precedents. By including these states, same sex marriage is now allowed in 30 U.S. states, up from 19 U.S. states before today.
And, the rulings may tip the balance in the 6th (which is home to four states, none of which has legalized same sex marriage) and 9th Circuits (home to nine states, four of which have legalized same sex marriage) where rulings striking down same sex marriage bans are pending, adding more states to the total. The 9th Circuit was widely expected to allow same sex marriage in any case. But, the 6th Circuit has seemed to be leaning towards refusing to strike down the same sex marriage ban, something that might change now.
[Update October 7: The 9th Circuit has made its precedent invalidating same sex marriage bans in cases out of Nevada and Idaho. This brings the total number of states that allow gay marriage or are in circuits invalidating same sex marriage bans to 35 plus D.C., out 51.]
[Update October 8: Every state in the 6th Circuit which awaits a fully briefed and argued ruling with a known swing vote judge (Judge Sutton), and outside the 6th Circuit Florida and Texas, as well as many other states, have trial court rulings striking down same sex marriage which are stayed pending circuit court rulings. A 9th ruling in Idaho is stayed pending an application to the U.S. Supreme Court for review, but the 9th Circuit ruling is not stayed in Nevada.]
Colorado's attorney general has relented and agreed to end to stay of a state court ruling striking down the same sex marriage ban in Colorado.
In principle, the U.S. Supreme Court could take up a case in the future and rule otherwise, invalidating rulings striking down same sex marriage based upon federal law in all fifty states. But, given the multiple circuit court ruling on the topic which it has declined to review, this seemed unlikely.
The 5th and 11th Circuits have no states where same sex marriage is currently allowed and no circuit court rulings on the subject. The 8th Circuit has two state where same sex marriage is allowed, but not circuit court rulings on the subject.
Notably, this ruling defuses what had been a key issue in the state attorney general's race in Colorado.