It's about time they heard this. I think half of it is obvious and the other half, not so much.
Whether or not states must recognize gay marriages performed elsewhere is obvious. I think they decide that states must recognize all marriages performed in other states. The precedent is there and it's just common sense.
The second issue - whether or not states are required to issue same-sex marriage licenses - is more complicated. I don't think they can decide that purely on the same-sex couples marriage ground. Rather, I think the decision there will be on marriage in general. And I don't know if they think that they can regulate state definitions of marriage from the federal bench. I'm curious how they handle it because it will set precedent for all other forms of marriage.
But in the end, that issue won't really matter. If states are obligated to observe the marriages performed in other states then same sex marriage becomes legally protected around the nation so long as 1 state performs and recognizes them. Given that 36 states already allow gay marriage, it's pretty much a resolved issue and this just puts the final stamp on it.