I'm a long-time Linux user and I use a PowerBook for admin and development duties. (I also admin Win2K machines with it.)
It's really outstanding. I can NFS mount drives in either direction, allowing me to pick the most convenient path of building on my laptop or on my dev Linux box. The PB comes with X, so I can fire up any Linux GUI tool I need. I have bash so I can script everything I need. And, best of all, I can mimic my run environment (Tomcat and PostgreSQL) on my laptop for completely portable development.
Hey--guess how I back up my laptop! I use a cron job that invokes rsync over ssh to a Linux box. Oh, the joys of having a Unix-based laptop!
The only awkward part would be switching between Sys V and BSD style commands (ps -elf vs. ps -aux, for example).
Highly, highly, recommended.
White dwarf seeks red giant for binary relationship.