The California Supreme Court had to uphold Prop. 8. Courts shouldn't overthrow elections. (In California or Florida) For the advocates of gay marriage, the solution is the same know as it was before - Organize, Agitate and Educate!
This issue is best decided in the legislature or at the ballot. The margin of victory for Prop. 8 was slim. The proponents should be on every state-wide ballot until they win, which will happen soon.
Paul Krugman recently wrote (on another issue) "California, it has long been claimed, is where the future happens first. But is that still true? If it is, God help America." And I would sadly agree. We aren't leading the nation (if we ever did).