Game center sync between iPad iphone

How do I sync game progress between an iPad and iPhone? Who cares about the leader board in game center? I want to pick up my iPad and play where I left off on my iPhone. I have read something about nsuserdefaults but I don't seem to have x code on my Mac. I don't want to get into reconfiguring the code and screw something up. Something like this should be simple for apple to fix.