I have (and use) both.
I'm on my 12" PowerBook G4 right now, which is my favorite computer ever. It is the PERFECT size.
Also on the Mac side, I own a Black Core 2 Duo MacBook, which does not have all my stuff on it yet, I'll most likely do that when I catch up on sleep.
All of my personal desktops are PCs, just because I love overclocking and the whole thing behind that.
In my opinion, Apple makes the best notebooks, while a self-built Windows PC is usually the best on the desktop. Mac Pros are nice, but I don't do video rendering or anything to justify it.