Well I use a PC for the main studio and a Mac Lappy for when I'm on the road. Now bear in mind I'm using a Powerbook (the Macbook Pro is alot faster), but I find that tracks I make on the road are often made alot simpler and quicker, because I have to think about CPU constraints, battery and also there are alot less plugins out there for the Mac (legit and illegit)...
When I make stuff on the PC, the power I have at my fingers is alot more, it's alot less glitchy and I'm forever messing with quirky plugins. I tend to get less done in more time ;)
Looking back to two years ago, both machines cost me around £1400 each. My PC was pretty top of the range then and put together based on my experience with PC's over the years (ie all the tweaks, the good hardware etc etc)...
At the end of the day it's up to you. I would say Mac shits all over PC for business related stuff, ical, isync etc etc all really are great. I am much more organised in my normal life cause of ical etc... Also for web design and coding I find it great, especially with terminal.
But for music, I don't know where I'd be without the PC. And I really hate Peak (of course Mac doesnt have Soundforge). A mac makes you focus more on simplicity as far as music goes which is very good, but there's been times when I've just been so annoyed because I haven't got something with me on the road that i have on the studio PC....
hope this helps....