When I first installed HD, I was asked about turning on PA, now with the exception of the trophy, I won't be using PA myself for two reasons.

Reason 1: PA doesn't allow me to make daring manouvers in races such as BR boosting the last straight of Moa Therma and the like, if I screw up, its my fault and thats the risk I run for racing the way I do.

Reason 2: I have always found the autopilot tends to disengage in harsh corners, not drive through packs of mines and bombs or even try and ram opponents in a tight pack. If its the same AI system then methinks I'll be turning that particular feature off lol