Faster than wind

How fast can you go in a vehicle going downwind in relation to the wind, using only the same wind for propulsion? Can you actually go faster than this wind, overtake it?

This is an interesting Wired story about someone who proves that you can achieve up to 3.5x or 2.8x the velocity of the wind. The real speed is governed by a number of factors, including friction and the strength of the vehicle itself:

http://www.wired.com/magazine/2011/02/ff_fasterthanwind/all/1