Based on what I've been reading about the Justices, I'm not so sure if they'll issue monumental sweeping rulings. I mean, sure the more liberal Justices will probably want to do so; but in the current state of things (including the fact that they are a minority on the Court), may leave it to technical standings that would validate the lower courts' rulings on it.
Effectively meaning, they may not have to issue a major sweeping ruling until much later in the future. This is at least in the Prop 8 case. DOMA may probably have parts of it struck down in a narrow provisional ruling; specifically the ones that pertain to legal and tax benefits to married couples. I see DOMA much more likely to be struck down as a whole than Prop 8 getting a sweeping ruling.
In effect, I say the Justices MAY prefer this than forcing outright change on a sensitive issue (even with the numbers showing American GP having much more positive support for same-sex marriage); leaving the constitutional issue to a case-by-case to the states while giving legitimately married same-sex couples the same federal benefits as heterosexual ones.
I do hope that they actually do a major sweeping ruling for Prop 8 and other states's constituational ban on same-sex marriage so this issue will be resolved at last. DOMA is a easier one at least.