As a member of the Church in good standing I do not believe that unmarried couples should be doing anything that would lead them to breaking God's law of chastity. President and Sister Clark's inspiring devotional spelled it out simply. I felt the Spirit's touch as I read their talk (I'm currently in Portland and I was unable to attend).
However the following story has me conflicted. In this situation, I do not believe government should be telling folks how to live, yet, I believe EVERYBODY, Latter-day Saint or not, should be chaste.
On the other hand, I believe N. Dakota has a right to do what they want. If they don't want unmarried couples living together than they can enact a law — I would hope that it goes to a general vote however. In this case, the citizens of that state definitely need a chance to weigh in.
At heart, I feel this law infringes on a person's basic right to make decisions about their own life. Also, I believe marriage is a purely religious institution and the secularization of it takes away from its importance. People shouldn't get married just because the law tells them they should. They should get married because of their love for each other and their love for God. I don't think God cares for a couple who gets married just to legally live together and then get divorced when they're done.
Perhaps the ideal situation is to have government stay out of things, and to have individual citizens, churches and communities work with each other to create societal contracts.