Intermittent reinforcement is illegal as a pay method in some jurisdictions, and even illegal in the form of slot machines (aka gambling) in some jurisdictions, because it is pretty much the best reinforcement schedule to use when you want to wean the workers out of being paid without having them quit...
Yes think Twitter. And yes it is the best reward mechanism. I will propose Netcoin adopt this mechanism now that it is a proven success with the Primecoin case study.