It will run on Intel or AMD, just like Windows and Linux do. AMD has all of the same instruction sets as intel does, they are both the x86 architecture, and they are both currently making chips that support SSE3, as well as all of the other older optimizations for this architecture. IBM made a concious decision to refocus their attention with the PPC to the gaming world, where they found with the Xbox that the $$$ involved is far more lucrative then 2-5% of the computer market share that Apple has. Apple simply didn't want to pay the extra cash necessary to have IBM engineer a competitive G5 chip for mobile computers.
That said, you all should take notice that Steve Jobs is extremely good friends with the Intel CEO, as he used to work with him closely back in the days of NeXTSTEP x86. Don't tell me you didn't see this coming...