I too have thought of this topic and have wondered if you can charge up the bike wile pedaling and using the regenerate button while going down hills, can you actually end up with a full charge after a days ride if you use the assist judiciously? And if you can, would it still be considered cheating? After all, you are putting in more effort when riding normal to make up for the assist up hills but still end up with spending the same energy? No? (I just ordered my BionX 350 and have never ridden with it so don't know if recharging to the full would be possible but that will be my first test).
EDIT; and yes using the throttle only IS cheating, but so is pedal assist if you don't actually recharge the battery with just pedalling and downhill regeneration... JMO