Maine became the fifth state to permit same-sex marriage, and the second state to do so by democratic vote of the state's elected representatives.
As I mentioned when Vermont made the same change, it is highly significant that the change is now taking place by democratic vote. That two states have now done so really takes the sting out of conservative arguments that same-sex marriage is being involuntarily imposed on a reluctant populace by unelected judges. The people of these states, speaking through their elected represenatives, have accepted same-sex marriage as appropriate.
It's amazing how much movement there has been on this issue in such a short time. If memory serves, it was only ten or so years ago that anything like marriage for gay couples appeared impossible. It didn't take long for civil unions to become a moderate, mainstream position, even though actual marriage remained a point of difficulty. Now, legislatures are accepting actual marriage.
One of the latest contrary arguments is that permitting same-sex marriage somehow discriminates against religion and will somehow require churches to recognize same-sex marriage even though it is contrary to their religious tenets. But a simple perusal of the actual bill shows that it amply protects against this danger.