Elaina,
Don't mean to scare you. We've used airtran many times without problems, but I've read again and again of flights being cancelled (and not knowing until they get to the airport) and have had time changes before, but never like the one they tried to do to me this time. I know for some it is not possible to fly in the day before, stay at a hotel and then get to the port (all added expenses), so they do this with no problem. I like airtran, but this time, I opted to cancel and get a refund (as we are actually staying at Disney afterwards and got cheaper flights elsewhere).
You didn't scare me as much as make me more alert! I'm just gonna keep checking on our flights and if they change anything I'll just cancel and book with Southwest. I'm sure people have had bad experiences with them as well but I've flown them from Bwi to mco soooo many times and (knock on wood) i've been okay each time!