Is that the Prop 8 case where the evidence was down right amusing?
Yes.
If the USSC strikes down Prop 8, it likely won't affect the rest of the country at all. It's been a while since I read the 9th Cir. decision, but it sticks in my mind it was struck down there based on "you can't give rights and then take them away." (CA has previously allowed SSM, then Prop 8 passed.) If the USSC does strike down Prop 8, it will likely be on those same grounds. Meaning that states that have SSM will keep it, but those that don't have it will be in the same boat they are now.
As for the other case, as I understand it, it also won't directly affect states that don't have SSM. All it will do is allow people who live in those states with SSM to get federal benefits that they are eligible for (Social Security, vet benefits, etc). I also think it would allow people who are in a SSM who work for the federal government to put their same-sex spouse on their health insurance. (Not sure on that last one.)
What striking down DOMA would do is set up
Loving v. Virginia, Part II. A couple could marry in a state that recognizes SSM, then go back to a state that does not and file under the Full Faith and Credit Clause of the US Constitution. (That's exactly what the Lovings did. They married in DC - which recognized interracial marriage - then filed suit in Virginia, where they lived.)
My prediction: 5-4, Roberts, Scalia, Thomas, Kennedy, Alito in the majority, Scalia writes the opinion, and possibly words it to declare gay marriage itself outright unconstitutional.
Unlikely. Kennedy has written opinions favoring gay rights. (He wrote
Lawrence v. Texas, for instance.)