Just when Apple’s PowerBook line was getting nicely settled, they go and confuse things by upgrading the iBook to a G4 processor. This was needed – the G3 was getting a bit long in the tooth, but it used to be the main thing that defined the difference between the iBook and Powerbook ranges.
I don’t imagine they’ll be upgrading the PowerBooks to a G5 in the very near future, so it’s almost a question of how much you want to pay for the nice shiny colour… 🙂