All of the experts thought that Barack Obama would win the New Hampshire primary. Perhaps more significantly, the prices at Intrade, the political prediction market, suggested that Obama was overwhelmingly likely to win. Many of us have been quite excited about the potential of prediction markets, in which people "bet" on political (and many other) outcomes. Such markets have a terrific track record in politics and elsewhere. And yet Clinton was a huge underdog in New Hampshire. Should we conclude that the prediction markets are unreliable after all? That nobody knows anything? That polls themselves mean nothing?