How accurate was he down to individual districts though? I think most of our elections are rigged on a higher level than an individual agency's actions but there have been close elections where a few well thought out placements of CIA rigging ops could have (or maybe did :)) changed the outcome of major elections.
Nate Silver doesn't forecast House races because there isn't enough good polling data. He does predict Senate races; he was 31 for 33 in 2012. He predicted that Republicans would win in North Dakota (a 92% probability) and Montana (66% probability). Democrats won both races.