Just a pointer to the Freakonomics blog wherein Leavitt exposes the idiocy of the well-circulated "don’t buy gas on Sept. 1st" email.
His final point is right on. Don’t encourage people to not buy gas for a day–encourage people not to use gas. Walking, biking, carpooling, public transportation are all great alternatives. I know I sound like a total hippie, but…I am. 🙂