On the same Powerbook, my first install of Leopard was really sluggish - it was very disappointing, even with all optimisation. After trying Tiger, various Linux and MorphOS I went back to Leopard and it was much faster - no idea why, obviously something strange happened on the first install, so there's always that possibility?
I find when I move from my G5 to any of my portables, I adjust to the speed difference after a while and get used to a different pace and there's stuff I just won't even try to do.