AAA isn't a big fan of this. If you over inflate your tires, they might rupture or blow. Putting the car in neutral could slow you down if you need to accelerate fast. And turning off your engine completely likely cuts off power to your steering and brakes. So it's far more difficult to control.
But a West Des Moines hypermiler (who doesn't draft, by the way, because he says, it's too dangerous) says he saves 20% on his monthly gas bill. That is 20 bucks a month he keeps in his pocket. He is an actuary, a man who works in numbers and risk every day. And he says hypermiling is definitely worth the risk. Do you?