Noggin & co,
*looks slightly worried* When on downwind you are going in the same direction as the wind. However, the wind will never be flowing over your wings from back to front unless you are happily flying your circuit one day and the winds whip up to around 120kts
In which case you lose lift and come falling back to mother earth.
Also remember that the names of circuit legs aren't always representative of the situation - for example if you took off with a slight tailwind, you would be flying into wind on downwind even thought the names always stay the same.
Seeya,
SpeedBird22