Yes, of course. Most people still use their CPUs.
Both PS3 and GPUs can't exchange CPUs. The Stanford folding team is so heavily promoting their new ways to compute proteins that many people get the impression that folding with regular CPUs is useless compared to the newer ways to fold. But that is wrong!
There were some discussions in the folding@home forums about this. The point is that the GPU client can fold just one type of protein simulation, the PS3 another and the SMP a third type of simulation. However to succesfully study proteins and find cures, you need a huge number of different simulations. Those are only possible via the CPU client.
Don't get confused by the Teraflops numbers, in reality they mean nothing to the science done.
Tom