This thing stuck me entirely differently, as I have been disagreeing with another poster at Prius Chat about whether Toyota ought to be (even) asked to pay for post-warranty failures in the PS system.

Electrical PS depends on some sort of torque sensor to determine how much (and in what direction) to add electrical assist. Toyota initially did that with potentiometers on a rubber plate. The problem was that potentiometers get noisy, and because assist may be needed 'promptly', only so much filtering can be done in the time domain. After paying for replacements under (and perhaps beyond) warranty, Toyota decided to use Hall Effect sensors instead. Whether or not led to this change by NHW11 problems (whiney NHW11 drivers), they have now got a system that works well and can make them lots of money in the future.

I do not know how much energy can be saved by electrical assist PS. Its major strength may be that it allows freedom in designing 'auto-stop' and hybrid vehicles. Toyota and other manufacturers will no doubt continue to use these systems.

DAS