Good news: Invensense has finally released a licence that allows open source projects such as ArduCopter/Plane to use the built-in sensor fusion processor in the MPU-6000 gyro/accel chip used in APM 2.x!
This processor, called the Digital Motion Processor (DMP), has been in the APM 2.x sensors from the beginning, but we weren't using it because Invensense had not specifically allowed their drive…