Some people may say 1/2 hour is not enough time to change planes in the Atlanta airport. I say 1/2 hour is not enough time to change planes in ANY airport. Too many unknown factors --delays getting to the gate, weather delaying the flight, how long it will take for you to get off the plane once they start deboarding -- can reduce your 30 minute layover to a 3 minute sprint through the terminal.
In Atlanta, all of AirTran's gates take up half of the C Concourse (about 18 gates in all) and they're relatively close. Still, if you come in at gate C-1 and have to get to gate C-16 and you're delayed by anything I mentioned, it would be tight. Is there another option with a longer layover?