well multiple processors are great - but you still end up paying for the power. And there is a limited amount of space to put processors inside a machine - and the heat sink? whoo baby, that would be a big one.
But one type of chip we'll eventually see in the near future <10 years will be a multiple CPU on a single chip - as the manufacturing process gets the size of CPUs smaller and smaller, a 8 CPU chip or even 16 CPU chip is possible. As long as the OS supports multiple CPUs there's no reason not to use them. I'm still waiting for the day I can do realtime radiosity of one of my animations....
Now that's ludicrous speed!
D