The FIA  has declared the double-decker diffuser designs used by Brawn GP, Toyota and Williams are  legal.

"International Court of Appeal - Decision  15/04/2009

The FIA International Court of Appeal has decided to deny the appeals submitted against decisions numbered 16 to 24 taken by the Panel of the Stewards on 26 March at the 2009 Grand Prix of Australia and counting towards the 2009 FIA Formula One World Championship."