What do you need that much power for? I know my iBook, with it's lowly 1.3 Ghz G4 is more then enough for what I do. (Which isn't saying much, but still.) Do you do video editing or something your PowerBook can't handle?
Occasionally
I want to learn how to program and my PB takes a long time to compile stuff
PB VS MB
GMA 950 < ATI Mobility Radeon 9700
15" > 13" (this is very important to me. just look at my signature. the screen sucks on both really.)
Mini DVI < Dual Link DVI (which my PB has)
Glossy < Matte (Glossy in car = big picture of the sun on your screen)
Core Duo > G4
Backlit KB > Standard KB (I actually use this a lot)
MacBook Pro fixes all the negatives of the MacBook over the PB.
I need more ram than a Core Duo MB can handle 2 GB is not enough. I know this from experience because I run out all the time on my PB. I have less than 256 MB RAM free with my normal workload open. If I add Photoshop of iMovie to the mix I run out quick.