Something that may not have been much considered on the Prop 8 case before the Supreme Court:
The California Judicial Branch created a "right" to marriage for homosexuals within that state. In accordance with the State and US Constitutions, the People of CA Amended their Constitution to overrule the judicial branch.
Should the US Supreme Court kill Prop 8, an Amendment to the CA State Constitution, the justices making that ruling will be cementing the power of the Judicial Branch over both of the others And over the people. Whatever their reasoning behind striking down that Constitutional Amendment, the effect will be that the Judicial Branch can no longer be overruled by any method and its power will be inviolate.
Basically, whatever the Judicial Branch declares goes and not even the Constitution can place limits on them.