The Prius that was in the news recently, here in San Diego, the conventional brakes were useless, and shifting to neutral wouldn't work, as it wouldn't allow it. What was successful, according to the CHP, was a very zealous tug on the hand brake (definitely an "emergency" brake in this case) as well as the foot pedal. The officer positioned his car in front, not to slow it down, but to prevent it from shooting forward after the driver finally got the car to a stop, despite it still wanting to move forward. Essentially the squad car was acting as a brick wall, but not a brake assist.

In this case, the car would not shift into neutral, nor did foot braking alone make a difference. It was muscle on the hand brake that ever so slowly dropped the speed.

You are correct about the first casualty. It was a Lexus and it happened in Santee, CA (part of San Diego County). The brake and neutral attempt were useless. The situation is described thus:

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California Highway Patrol Officer Mark Saylor, 45, his wife, Cleofe, 45, their daughter Mahala, 13, and Cleofe's brother Chris Lastrella, 39, were traveling on a freeway near Santee on Aug. 28 when their vehicle reached speeds of more than 120 mph, hit a sport utility vehicle, launched off an embankment, rolled several times and burst into flames.

Investigators found that a wrong-sized floor mat that trapped the accelerator was the cause of the crash. (Note, this has not been forensically proven, and is in dispute at the moment.)

A haunting 911 call captured Lastrella telling the others to pray before the car launched off the embankment.

...the Lexus ES350 "began to accelerate on its own." Saylor attempted to apply the brakes and do everything possible to stop the car, but he was unable to do so...
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The video demonstrated the "technique" on a relatively low horse power (and low torque) four cylinder engine. A Lexus ES350 has a 272HP V6 (at full throttle) and the Prius has a high torque electric motor. Good luck with that braking.

>> ^silvercord:
>> ^supersparky:
What this article fails to include are the unique issues with the hybrid cars. Oddly enough, two have gone out of control in my home city, San Diego. The first being a death, which started the publicity. This one was driven by an off duty cop! I would think his training would have given him these skills to stop the car. However, as more and more facts have come out, the brakes it seems are useless. The Prius uses a combination of electrical and mechanical braking. Unfortunately the mechanical only kicks in under a certain speed.
Many people have reported burying the brake pedal to the floor and it having little effect. They also seem to not be able to shift into neutral, as it's a drive by wire system. Many cars don't let you shut off the engine if it's in gear too.
The Prius, while being a butt ugly eye sore and gutless wonder, also has an electric motor. These have 100% of their torque at any RPM. This means a gas engine can be fought and stalled with functional brakes, but you fight the full torgue of an electric motor all the way down to stopping, if you're lucky.
No, a fail-safe override needs to be considered for all drive by wire vehicles. Something that actually physically disconnects power from the system as a last resort.

My understanding is that the car driven by the off duty officer was a 2009 Lexus ES 350. That is not a hybrid. That said, I tried the 'move the shift to neutral' trick yesterday in my Windstar and it worked just fine.
However, the link I provided also noted: Last month, Consumer Reports found that models that don't have so-called smart-throttle technology, which allows the brake to take precedence over the throttle, a vehicle might not have adequate brakes to overcome a stuck throttle at 60 mph.
So, jam your foot down on the brake and kick it into neutral, pray like hell that you hit a truckload of Snuggies.
As for the electric cars, maybe a nuclear air burst that issues an effective electromagnetic pulse would do the trick.