Several people have mentioned Airtran all being on one concourse. That is, indeed, the way that the airport is laid out. However, you can't totally rely on every Airtran flight arriving and departing from that one concourse. I recently flew home to Atlanta on Airtran from Milwaukee. We were an hour late (due to a medical emergency on the airplane before Milwaukee -- not Airtran's fault).
Anyway -- by the time we arrived on the ground in ATL, of course the planned arrival gate had long since been assigned to another plane -- there were other flights (on varying airlines) that were late leaving or late departing due to weather -- and so they were having to juggle the gate assignments the best they could. We were an hour late landing -- there were other planes trying to get into a gate -- and we then sat on the tarmac for 20 minutes waiting for a gate to come open. The gate that we finally got to was NOT on the regular Airtran concourse.
There were people on our flight who were making connections. They do hold the connecting flight when they can. But on that evening, the Flight Attendants told us that that was not a guarantee. Their connecting flights were on a different concourse -- and it was late in the evening, so some people were in the position of possibly having to wait until the next day to connect.
With a 50 minute planned layover, it really wouldn't take much to totally change your schedule. All it takes is bad weather in the Northeast, and it affects the entire airport. If you can go with the flow and would not be upset to miss the connecting flight and to hopefully get on the next flight, then go for it. But I think that in Atlanta, a 1-1/2 hr (or even 2 hour) layover is much safer. There are plenty of shops and places to eat if you need to kill time.