Even in light of their licensing agreement with Transmeta, I have a very hard time believing that we'll see a fully torqued Cell in a PS3. It's just a hunch, but they will have a damn hard time keeping the thermals in check @ 4.8 GHz.
Any Cell design cloaked within a PS3 will have the limitation of an ubersleek case that might look pretty, but will have to be very smartly engineered to control runaway temps at that kind of speed.
I think heat-pipe technology might be a given for the PS3 and the Xenon.