Today's ruling gave legal standing to the people who worked to pass a ballot referendum to defend it in court after California's state government had decided not to defend the law in federal court. That would have left Prop. 8 without a defense and opening the way to overturning its ban on same-sex marriages, which has already been ruled unconstitutional by the  U.S. district judge Vaughn Walker last year. His ruling, however, did not permit California to begin issuing same-sex marriage certificates whil it is under appeal with the U.S. 9th Circuit Court of Appeals, which has already heard arguments. The 9th Circuit was watching today's ruling in state courts closely, and with the state government's approval, it can continue to issue a ruling on the case's merits. Prop. 8 Tracker has more background on why the federal courts were watching the state court ruling:

Rather than immediately rule on those arguments, the 9th Circuit decided to kick the ball over to the California Supreme Court on the issue of standing, asking an important question: do proponents of ballot initiatives in California — in this case, those who collected signatures and raised money and helped pass the initiative — have the authority to represent the state when the state’s public officials decline to defend the initiative? If ultimately not, then Prop 8 goes without a defendant, our side (the plaintiffs) wins and Prop 8 ends.