I've been a PC guy forever but I bought a Mac Mini a few weeks ago and I'm hooked. It's so much easier to use. Everything is included (built-in wireless, bluetooth for the wireless keyboard and mouse, digital audio out, remote control, ipod interface, DVI to connect to the HDMI of my TV, etc.). I'm still working on the sound quality but it's pretty good already and I believe that ultimately there is little difference between a Mac and a PC in sound. It's simply a matter of how much effort is required for that sound.
I've worked measuring jitter for several years. (I'm not talking about too much coffee). Think of jitter as noise in the time domain. The DAC relies on the timing of the digital input signal. Timing noise (jitter) causes problems with the DAC timing. The result is audible. I think that virtually any computer output stream needs to be reclocked to get the best audio out. That applies to both Mac and PC. Ultimately, I think that someone will come out with a DAC focused on the PC audio market which will take care of the jitter problem.