I, also, agree with posters #5 and #6. There are many laws that states chose to recognize or not. Same sex marriage, being a very controversial issue, would be one which states would fight. Given many states have not recognized same sex marriages as legal, it would not surprise me that some states would simply refuse to recognize same sex married couples--as they do not now.
Therefore, if they had to be recognized, states would simply have to decide if it were worth the fight in their own state to fight against it. In the end, it would seem that al states would simply be required to legalize same sex marriages. (Unfortunately, I find this would not happen that easily.)