When I fly internationally, I always sit in coach. It's never been an option to move into business class. I've been lucky the last few flights to even have a window seat.
And when I fly domestically, it's usually from the Midwest to somewhere on the East Coast. Nothing usually more than about 90 minutes or so. And then, really, you can sit anywhere in the plane. I hate sitting in the back because I don't have the patience to wait for everyone else to get off, but really, you can sit anywhere for less than two hours, even squished in a middle seat between two sumo wrestlers.
Lately though, I've been trying to work down my AirTran credits. I flew a lot last year, almost all on AirTran and my credits are starting to expire. It only takes four credits to upgrade to business class and I think I've done that for most of my last five or six flights. It's a little bit of a waste for a short flight, but it's use them or lose them, and I figure they were given to me to use.
So what I've learned is that while I can definitely sit in coach and have no issues doing so, it's still nicer to sit in business class. The biggest differences - a bigger tray table and enough space so that you can use a computer or do some writing without sticking your elbows into the person next to you. There's probably even more leg room, but I'm short and how much leg room can a short person use?! The other good part is that there is a bathroom up front that is theoretically reserved for the 12 people sitting in the front of the plane. I'm fairly certain it is no larger than the one in the back of the plane for the other 126 people, but the idea that it's more available is a nice one.
Alas, AirTran flies from Chicago but not directly to any of the places I generally need to go. I need two more round-trips before April to get another year's worth of Elite status, which is nice to have even if I can't use it, so I'm sure I'll take at least another two trips. The question will be whether I still have enough credits left to sit in the front of the plane....