From AirTran's website:

Redemption of 50 credits for an A+ Travel Reward is required for one free coach roundtrip ticket for travel between the 48 contiguous United States and anywhere in Alaska, Hawaii, Canada and Mexico. Redemption of 100 Credits for an A+ Travel Reward is required for one free coach roundtrip ticket for travel anywhere else in the world served with no more than two connections each way. Free travel on other airlines will not be issued on routes where AirTran Airways publishes schedules and fares. On those routes, free tickets for one-way travel will be issued for AirTran Airways flights in exchange for redemption for the appropriate A+ Travel Reward.

Other details:
1) At least one Saturday night is required.
2) If you give AirTran your FF number on the other airline while booking, yes, you will get other airline miles.

Also, I don't know if people have been logging into their A+ accounts, but there are apparently some changes; for example, they show how many credits you've earned towards Elite status. So I get taunted each time with how far, far away I am from Elite. But still -- looks like the changes to the interface will help.