2,200 will join the already 336 hooked up in Rome, New York. They're interested in the architecture of the Cell Processor, not Uncharted 2.
They use them for various things like improving radar imaging and processing high-def video feeds, as well as exploring what possible applications could be developed using the Cell Processor, like maybe an automated defence network of some kind.
Who knew the PlayStation would give us our own John Connor? Rock on U.S.A.F.!