I have yet to see a convincing argument either way. I am a PC guy. My theory is that if you aren't willing to do a little tweaking to get your PC right, buy a MAC. If you want more flexibility, lower prices, more options, and are willing to maybe do some research and tweaking, buy a PC. I don't need a dual processor G5, my AMD 64 bit processor system runs every bit as fast and smooth and possibly even better. My PC gets used hardcore about 60 - 120 hours a week with no crashes. I can boot up and start up Nuendo and get a file opened and playing in all of about 2 minutes. I too have a firewall, antivirus, Raid software, weather applet and all sorts of crap running in the backround. The biggest thing is to know windows a little and know what crap you are and aren't putting on your computer and how those different programs affect each other. I have absolutely no problems with either mac's or PC's. It's just like cars. There are lots of options, some cheaper, some more expensive. No 1 is better than the other, but just serves a different purpose. The thing is, no matter what you have, you have to treat it right and take care of it. If not, it will not run properly, or even at all.
I would never choose between a Mac or a PC. I would look at the software and hardware I want to run on it and then decide which platform fits it best. If I want MOTU DP4 or Pro Tools or the new Logic, I would get a MAC. If I want Nuendo or Cubase or Audition or Sonar, I would get a PC.
As far as networking towers to share audio demands between different computers, Steinberg has been doing that for years. In fact, I think you can even do it between a MAC and a PC.
For me, anyone who flat out says that one is better than the other is just trying to make themselves feel better by defending their own purchase. Or else doesn't no how to properly use the other system.