Regarding gay marriage, Michael Kinsley has an odd suggestion in the "never gonna happen but it's an interesting way to look at the problem" category.
One of the complications that will hover over most discussions of gay marriage is that most people in this country really don't believe in State's Rights. Some say they do, generally because they think they can win certain emotion-laden battles in a smaller arena. But when they lose — say, when the voters in a state elect to have medical marijuana or assisted suicide or gay marriage — they immediately want the Fed to step in, enforce some higher law…or if there isn't one, make one.
The concept of gay marriage makes the whole concept of State's Rights dicier, since states are supposed to honor each others' laws. That hasn't been a big concern with other issues that seem to be in play, since you can only smoke medical marijuana or assist suicide or abort a fetus in one state at a time. But gays who marry in whatever state first recognizes gay marriage would want to travel, perhaps relocate, maybe buy insurance from companies in another state, etc. And if you give Sam and Fred the right to marry in a state and they do, what happens to their union if the voters of that state later repeal the law?
I don't know what's going to happen here. But I do know it's going to be messy.