While somewhat off topic from this thread, It seemed like a good place to offer my experiences. We got our Hybrid in late April so it's somewhat under five months old. I've read the notes about this wiring harness issue and just received the recall for it yesterday.

Interestingly, we experienced the same symptoms as the faulty wiring harness after about three months. We took it to the dealer and the service manager diagnosed a problem with the "Hybrid Control Module." They replaced said module, reprogrammed the system and the Check Engine and Battery light problems disappeared. We called to see if the wiring harness issue applied to us and they confirmed that it did.

Anyway, as far as the Control Module is concerned we have noticed neither negative or positive as far as gas mileage is concerned. However, during acceleration the Assist meter flies to the right more than it ever did and there is a perceptible improved feel of acceleration. As someone else also reported, we can see the vehicle charging at certain consistent speeds when the Eco light is on (this didn't happen as often prior).

Hope these comments prove informative.

Cheers!