My 15-inch G4 Powerbook arrived last Thursday, I'm now moving all my development and office environment to it (from Linux).
I'll be working in at least three different locations in the next few months, and after looking at the options for a high-powered laptop for software development, the Powerbook is the clear winner: you wouldn't use Windows for this (at least I wouldn't), and setting up Linux on a laptop until everything runs properly takes a lot of work.
Although I've never used a Mac before, having BSD inside makes it very easy to switch to if you come from a unix/linux background.
Wow, all my stuff in this small case - brings distant memories of my first IBM "sewing machine" portable...
Here we go - let's hit Fink to get started!