Do campaign promises mean anything?

Jake Tapper of ABC News asks a relevant question on his blog.

Are we supposed to act as if things politicians say during primaries are irrelevant and meaningless? Are we supposed to just accept as fact that politicians say things in the heat of the moment that they don't mean and thus we should should just collectively self-induce amnesia?


President Barack Hussein Obama's (D) trip to Canada, our friendly neighbor to the north, inspired the question.  Tapper remembers during a campaign debate Obama promised

I will make sure that we renegotiate (NAFTA)," then-Sen. Barack Obama, D-Ill., said during the Democratic debate in Cleveland, Ohio on Feb. 26, 2008. "We should use the hammer of a potential opt-out (of NAFTA) as leverage to ensure that we actually get labor and environmental standards that are enforced.
But that was then and as Tapper noted this is now so that is
Language You Likely Won't Hear Today from President Obama in Canada
When reminded or questioned about statements or promises made during the heat of the campaign
"This is fun for the press to try to stir up whatever quotes were generated during the course of the campaign," President Obama said during his Transition in early December, when a reporter asked him about criticisms he and now-Secretary of State Clinton had made about each other's foreign policy views.

"They're your quotes, sir," said the reporter, Peter Baker of the New York Times.

"No, I understand. And you're having fun," Obama continued. "And there's nothing wrong with that. I'm not faulting it."

So are these promises made in the heat of a campaign just a game?  Just made for fun and not to be believed? What about promises made while in office?  What about the promise that the porkylus bill contains no fat? 
Discuss endlessly.