I must agree with Mankiw. I must also say I am very impressed with the guy sitting immediately behind Colbert who doesn't laugh, smile, or maybe even blink during the entire 5 minutes.
Best lines (paraphrased)
"If we want to stop bringing illegal immigrants to pick our fruits and vegetables, there's a very simple way: stop eating fruits and vegetables."
"It was the ancient Israelites who built the first food pyramids."
"Apparently even the invisible hand doesn't want to pick beans."
Oddly enough, the only line that actually got a laugh was about Dems and Reps working together "as they always have."