From the Commodity Futures Trading Commission website:
Washington, DC – The U.S. Commodity Futures Trading Commission (CFTC) today filed a civil complaint in federal district court in Washington, DC, charging Intrade The Prediction Market Limited (Intrade) and Trade Exchange Network Limited (TEN), Irish companies based in Dublin, Ireland, with offering commodity option contracts to U.S. customers for trading, as well as soliciting, accepting, and confirming the execution of orders from U.S. customers, all in violation of the CFTC’s ban on off-exchange options trading. ...Why aren't prediction markets a form of free speech?
Update: Harry Eagar points out that Intrade claims that it will be back shortly with a U.S. compliant platform.
HT: Marginal Revolution