I just got through building a nice PC setup, but I have to agree. I used to use a g4 a few years back, and core audio/midi is something special.
The way you can use audio/midi devices, create aggregate devices, route audio all over the place, etc...is definitely dope.
I'm happy with win7 for now, but I still plan to get another mac in the setup, even if it's just a mac mini, I can run all my vsts via ethernet into the mac, have the pc handle all the heavy lifting and keep the mac lean and mean.
Now THATS good advice!