I spend a gorgeous morning at the field with Jason Short testing code and tuning PIDs. He was focusing on ArduCopter 2.0.40 and I was just dialing in the PIDs for the HobbyKing Bixler, which is our current recommended platform for beginners.
I think I've got them pretty close, so I've posted the config file in the manual here with the rest of the config files for standard aircraft. Just load it in the Mission Planner and write it to APM, and you're ready to go.
Here's the RTL circle: