I haven't switched so much as tweaked.

My P2-400 is still running Debian Etch as a headless server in my spare bedroom closet.

My dual-boot Power Mac (circa 2001) runs Tiger and Kubuntu (used to be Debian).

My Powerbook (still a G4) runs Tiger, but I'm saving my pennies for a MacBook Pro. I'm itching to try out Parallels or VMWare since there are apps I use for work that are Windows-only and we use VMWare at school to set up lab infrastructure for our networking students.