Cuc's got it solid. Any machine that bootlegs for speed by executing five instructions per hertz or so instead of one is asking for trouble; prioritizing makes it much easier to crap the bed, and much easier for say, your IM program to screw up your audio editing program.
But I agree--the Mac is a niche machine, and it has a lot of strong points when operating within the right environments. As personal computers, though, I don't think they excel.