For applications which don't need much RAM per node or double-precision calculations, the PS3 is a very cheap way to get computing power.
Compare it with getting a Cell server directly from IBM, which surely costs more than $1000. Sure, the IBM server will have more RAM and a faster Cell, but for $299 you get a pretty good one already.
My Mario Kart Wii friend code: 2707-1866-0957