I use Windows XP Pro on my Dell Precision workstation (Xeons omg!), Mac OS X on my older G4 (mirrored drive doors omg!), and Ubuntu on my Compaq netbook. Both the workstation and the Mac are used to make music, but I pretty much only do softsynth-related stuff on the Dell (I do very much prefer hardware, but my budget does not allow me to purchase a $300+ synthesizer whenever I'm looking for a specific sound) as opposed to actual recording on the Mac.
I find that the Mac plays nicer with my outboard hardware than the PC does. My midi interface is literally plug-and-play on the Mac, no drivers needed.
On the PC it was more like Install Drivers, Plug In, Continue Installation Process, Think It's Working, Oh No Why Is Windows Asking Me To Install Drivers For It Over And Over Again, Restart Even Though I Shouldn't Have To, Windows Asks For Drivers Again, Oh Wow It Works, Play.
Oh well, at least I can play games on the Dell. I also run Xubuntu and FreeBSD in VirtualBox on it. If
Wine wasn't so difficult on Linux I'd rather be using it on the Dell. I find Windows to feel pretty vulgar and, well, ugly (in more than just a visual sense) when it comes to the user experience.