As I understand it, Atlanta is the largest air hub in North America, so chances are, if the DUmmy doesn't fly OUT of Atlanta, he will end up connecting THROUGH it. I changed planes there once, but I was only a kid, and hardly remember it.
I have connected through Chicago several times in recent history. It always seems that your layover is extremely short, and your connecting flights are at opposite ends of the airport. Not once have I not found myself huffing and puffing to catch my connection, while hearing my name being called over the PA, because the flight was about to leave.