I totally agree with Davidlove,
I am a dual platform user. Every day I site in front of a P4 PC, and a Powerbook 15" 1.5Ghz. OS-X is the difference, it blows windowz away...do your research. 2 years OS-X no system reloads..... 2...
Realistically we can expect too see a low voltage G5. The G5 architecture is going to really get rid of a lot of bottlenecks in the current G4. Bus speed among many others.