Party Poker is official:
http://www.partygaming.com/images/docs/061001_USLegislation2.pdf
They say that if it is signed by the President (they expect it to be in the next two weeks) they will stop all US bets immediately.
Can’t see that this is knee jerk, they will have taken the best advise on the planet about this before coming out plublicly and making this statement.