Dude I'm telling you man it all depends. I always say that, how liberally will you be using the internet? I've been a mac user since 2006 and I'll never switch over because I use it not only for mixing, but for facebook, ripping media (typically Payperviews), watching anal sex, and downloading random shit that I don't even know what it. But the way I see it is if you're using your computer completely for mixing, I say go PC. I mean you save a ton of money going that direction. But at the same time, I haven' used a PC since 2006 so I don't know how reliable the OS is nowadays, although I heard Windows 7 is light years ahead of what Vista was.
Edit: I forgot to mension, going PC will not only save money now, but it will save money long term. You can upgrade them much more than you can macs if you build your own. I'm telling you man, If Apple would let us build our own mac's, it would dominate and end this PC vs Mac debate
But Apples OS is enough for me to go with a mac