After reading this NYT article on the Corzine campaign's attempts to make an issue out of Chris Christie's weight, I think I'd have to answer yes:
In the ugly New Jersey contest for governor, Mr. Corzine and Mr. Christie have traded all sorts of shots, over mothers and mammograms, loans and lying. But now, Mr. Corzine’s campaign is calling attention to his rival’s corpulence in increasingly overt ways.
Mr. Corzine’s television commercials and Web videos feature unattractive images of Mr. Christie, sometimes shot from the side or backside, highlighting his heft, jowls and double chin.
Meanwhile, Mr. Corzine, 62, is conspicuously running in 5- and 10-kilometer races almost every weekend, as he did last Saturday and Sunday, underscoring his athleticism and readiness for the physical demands of another term — and raising doubts about Mr. Christie’s.
Prejudice against the overweight is, of course, the last socially acceptable prejudice. Throw in the fact that, as the NYT points out, New Jersey is a pretty lean state (it's ranked 42nd in obesity) and you can see how, despicable as it may be, this could be a winning tactic for Corzine. I don't really know how Christie can counter it. His attempts to slough it off with good humor are, to me at least, kind of winning, and certainly sympathy-inducing; then again, he's falling in the polls.
It seems like Christie's best bet could be to take Corzine's anti-fat stuff and turn it back on him by trying to turn it into a class issue. Try to make Corzine's physical fitness of a piece with his tenure at Goldman Sachs. Use it to paint him as an out-of-touch Wall Street malefactor. Maybe a commercial the features shots of Corzine running road races followed by, say, pictures of John Thain in road-race gear.