We flew Dallas to Orlando last Sept on Airtran and had no problems.
There are a couple of things that may have contributed:
1) We flew on a Tues. (Sept 11)--supposed to be lower-traffic day AND it was 9-11. This was on purpose.
2) We were on the first flight of the day--this meant that we got a "fresh" plane (cleaned, etc.) AND it also meant that there was not time for delays to build up.
3) Because of #1 and #2 (I guess), we were on a plane with about 11 other people, which was cool.
We flew American on the way back. That was the latest flight of the day, it had a small delay (30 minutes or so?) AND it was pretty full. No real complaints, though. In fact, the plane had TVs in it, and they showed Wild Hogs. It was nice having a diversion while my kids fell asleep and it was too dark outside to see anything. BTW, I saved $1.99 (or something like that) by using my FREE Airtran headphones to listen to the movie on the American flight.
I would not hesitate to fly Airtran again. In fact, I considered booking another DIS trip this Sept with Airtran, but we decided to put it off until next year.