[ethanhunt_]

When a car with power-steering loses power, it doesn't become like a car without power-steering. I've had a car shutdown at highway speeds, and turning the wheel is incredibly difficult. At the time I was a fairly muscled weightlifter, and I could not turn the wheel more than a few degrees (I managed to change one lane into a turn off).

mzr's comment above gives good advice: don't turn off or remove the key in a moving vehicle. Shift to neutral if the gas pedal is stuck.

[tadfisher]

This is correct. In cars with hydraulic-assisted steering, you're forcing fluid back through the pump, which is quite hard to do in addition to the fighting the bulk of your car and steering rack. In cars with electric-assisted steering, like the Prius, you're working against the electric motor using a belt and pulleys.

Which begs the question: why isn't the electric-assist motor designed to freewheel when power is lost? Losing steering assist at speed would be a more manageable situation.