With Apple announcing its next OS today. Snow Leopard can only be installed on Intel macs, no PPC included.
Read more about the requirements here: Clicky
PPC made a good run, but Intel's finally taken over.
At first I was really unhappy to hear of the PPC demise. However, that has changed. RISC was/is good for embedded or single purposes machines. Like a gaming machine, a car's internal computer, or an internet router. It seems to be a perfect fit and IBM marketed itself as such.
I am sure the PowerPC, Cell, or Power chip would have been fine for Apple if they had stayed on that roadmap but the G5 is over 5 years old and has become obsolete for many modern applications. The direction IBM was taking those chips was not really beneficial to Apple. Perhaps in the future you will see a Power-type coprocessor in macs but that is only my speculation. Who knows what Apple has up its sleeve for the next 10 years of computing.
What is fair to say is that Apple is embracing Intel 100% in snow leopard. I see Snow Leo as an optimization of the current OS before they move forward for the next decade. Jobs and Co have their roadmaps 10+ years out. I have a feeling the OS after Snow Leopard will start to shed more light and be a baby step in the new roadmap.
I am sure they will still call it Mac OS X but it will feel more like Mac OS XI as far as features. The only way to do this is by solidifying their move to Intel and lay groundwork for where they see computing going... With PA Semi and all the core goodness of 10.6 like grand central and OpenCL, who knows what is in Apple's 10 year future. Video recognition? Voice Recognition? CloudOS? Netbook? AI?