I think you can tell a lot about the candidates from these attempts at humor.

Edwards stuck to his roots.

Richardson and Thompson show an ability to laugh at themselves and the system.

Huckabee and Romney,,,,go figure!

MCcain needs a drink

Obama shows whats really bothering him. (his kinship to Cheney)

Clinton and Giuliani show a guarded humor similar to their leadership traits. (secretive and fearful of public critique)
I can just hear them, sitting around with their corporate buddies telling jokes; "Did you hear the one about the man whose job was outsourced to China?")

yeah all his bosses died of "lead" poisoning....