This is how it will play out, They said last night on the news that anyone in the Untied States can go to Cal and get married. So a gay couple from Ohio can go to Cal get married and then turn around and take it to their state court trying to get them to up-hold the stauts of the marrage.
The Defense of Marriage Act (from our dear friends in the Clinton Administration) states that states don't have to recognize other states' gay marriages.
If DOMA didn't exist, this decision would be irrelevant, because as long as Massachusetts had marriage equality, people from other states could just go to Boston for the wedding and have it recognized back home.
You have to live in MA to get a gay marriage, but I was saying people will go back to their home state taking it to the courts. I believe some state will follow CA and let gay marriages happen.