The US Air Force have already a PS3 (old generation) computing cluster of 336 consoles. But they want extend it with up to 2,200 new PlayStation 3 consoles for research into supercomputing.
It seems that they perform some "processing multiple radar images into higher resolution composite images (known as synthetic aperture radar image formation), high-def video processing, and 'neuromorphic computing'.
Source : link
Cell Processor spec : link