You can’t take a single poll on it’s own, but this CNN poll (data here) released at noon today does comport with the trend of Newt rising as Romney’s main challenger, and Cain feeling the effects of the negative publicity.
Update: Ed Morrissey, linking also to a PPP poll showing Newt in the lead, notes:
It looks like Gingrich has his opening. Can he take advantage of it? We’ll see now that the other candidates have an incentive to go after him — but Gingrich has played very graciously with everyone else in this race, and going negative on Newt might have a high risk of backfire.
And an Iowa poll shows Newt and Cain in a tie.