Well I have had my APM up and running for a few weeks now and have flown some nice long missions 10-14km with trouble free performance. The only real issue I have had is the homing like action between waypoints, even in nil wind. The aircraft will drift right of track and eventualy home back into the next waypoint, following an arc between waypoints. Just after a few tuning tips to correct this behaviour. Attached is a google maps plot of how the aircraft is behaving.