Politico has a detailed story about Nate Silver's move to ESPN/ABC: Silver to Espn
More power to Silver, although it's a blow to the NY Times.
Still, there's reason to worry:
1. As others have noted, ESPN is a sports outfit that has been burned by 'Politics' in the past (witness the messy relationships with Rush Limbaugh and Dennis Miller). While ABC news is part of the umbrella, it could cause the right wing to go nuts if Silver makes too much news on the political front while also appearing on sports broadcasts
2. Silver does have a background in baseball stats, but, athletics is still different from polling. The human factor, including just plain good/bad luck, has more impact in the sports world than analyzing polls. A few wayward predictions (such as first picking the Patriots and Seahawks would be in the Super Bowl - neither were - and then picking the 49ers to beat the Ravens - nope!) will color some folks' perception of his political skills, and make him easier to dismiss.
3. The Oscars. I am a hardcore Academy Awards prediction shark myself. Nate Silver has been bad, and occassionally, laughably bad, prognosticator of these golden statues in the past. Hollywood is not a numbers game. You can't divine insight from knowing which film won Best Sound Editing in 1983 and expect it to project for the winner next year. You actually have to see the movies and, more importantly, know how Hollywood works and thinks. Again, foolish picks in an area out of one's expertise could tarnish Silver's rep.
In the end, I wish Nate Silver well. He was certainly a voice of reason during this past political campaign (and in years prior). But, I also caution him not to spread himself too thin.