I use a PC for my graphics, and an Apple for my Audio. My take is this, I know my way around PCs, and have been using computers since they have been in home use, and just didn't like the hassle of getting my setup put together on the PC. Also I have tablets, scanners, 3d controllers etc, it was just a mess having SO MUCH connected. When I bought a laptop, I gave the MacBook Pro a shot, both my brothers had them, and I used Macs from the start, and move to PCs right at the release of the Pentium I. Thought I would see what's up.
Pretty straight forward. Spend a little bit less time fiddling with drivers and settings etc and more time doing what I want. But I don't like how OSX kind of hides issues. OSX is good at it, so when it crashes it's always catastrophic. And I've seen nothing telling me what happened. Just says you need to turn the machine off and back on. I look at the error messages after reboot, but meh. And it's nice fiddling less, but I feel like I really have to dig to get to options.. Overall it's a great machine, it's super stable, it crashes now and again, but that's expected with it on almost 24/7.
I like both, and I don't find them vastly different. Less tinkering with the laptop, but I feel less options. My desktop PC is great, and I hope with windows 7 that I can get it running with my audio setup. Would be nice to have a quad core with tons of RAM in case my laptop runs out of breath.
So yeah, it's all down to preference. Nothing else. I like having both. In a perfect world I would have a fast i7 desktop and a macPro at a desk with a KVM switch, or maybe a quad monitor setup with dual screens for each. A two by two verticle system. Then a fully loaded MacBook Pro running both OS.