A quick follow-up to my earlier post on this thread. I'm in agreement with the general conclusion that Mac or PC is just a question of whether you have a preference for one platform, you have something against a PC or aren't willing to pay the Mac premium. However, I'm backing away from my earlier conclusion that Mac has any advantage as a music server (or PC as a general computing platform).
The reason is the new iTunes 8 for PC. Despite the time and effort to set up Foobar I was appreciating it much more than iTunes because of the ability to arrange the elements anywhere on the interface, set the font type/size, control how the playlist behaves, switch the output methods (i.e. kernal streaming), use Secret Rabbit etc.
I still prefer the versatility of Foobar to iTunes, but after some longer listening sessions, I'm finding the output switching and Secret Rabbit with Foobar are not really improving my sound. Maybe when I have an Isabella, with more sensitive DAC I will hear the difference; currently I'm using a Scott Nixon tube + power source DAC and a NuForce Icon DAC section (BTW, I'm not impressed with either, but the KingRex T-20 DAC is quite good).
Also, with the new iTunes 8, the interface is just cooler than Foobar or the old iTunes; I especially like the mini-album art front end. Another reason I was using Foobar is that I heard iTunes was inefficient on a PC, but on my Centrino 2, 64-bit Vista machine, the resource meter shows the same reading, 6%, for both applications.
Therefore, I find no drawback to using iTunes on a PC. You can still have the conveniences and simplicity that Apple offers. As far as I can tell, the only real measurable factors are those mentioned at the top.