The contract that pays out $10 if Obama wins is currently trading at $6.70 per contract, implying a 67% chance Obama wins vs Nate Silver's 90%+.
Unfortunately, Intrade and American gambling regulations don't play nice so they don't accept US transactions. They also won't write you a margin account so you actually need to have funds in their system to execute a trade today.
Hard to say which party is inaccurately estimating the outcome, but given the regulatory hurdles around Intrade and the seemingly low volumes, I wouldn't be surprised if they're off.
SkyBet and Ladbrokers for example both have payouts closer to 538's forecast.
What is peculiar is that Intrade is the outlier. In a liquid market this shouldn't happen because it allows for risk-free payouts. So something seems a bit odd about Intrade.
It's possible the campaigns have caught on to Intrade's impact on the media and will now step in when prices fall to much. </conspiracy>
IEM (http://iemweb.biz.uiowa.edu/quotes/Pres12_quotes.html) and Intrade were up until yesterday off by 10%. Eventually things moved closer, but regulatory hurdles in actually getting money in (+ limits on funding) really hurt arbitrage opportunities.
Also of note is that other betting markets were consistently higher than Intrade was for all of the last 6 months basically- there are a lot of theories as to why this may be, but it's regularly been 5%+ lower on Obama.