The Atlanta hub is a HUGE airport. I've been there about 3 times or so usually flying Delta, and I can tell you that you could easily get lost for 3 hours roaming around that airport.
Now, what's kinda cool about it is these trains that move about within the terminals. You can have a jeuvenille moment and just ride the trains from one set of terminals to the other (its kinda like those kids who just want to go up and down the escalator over and over, only mildly more interesting). They have a decent amount of little shops and cafes to keep the average person busy for a while. Its not so boring in my opinion.