I don't get it either. Typically, they compete for different parts of the market with Apple's costing 2-3x as much as an entry level Vista as far as laptops go. I love the look of a Mac laptop (my Gateway laptop is an ugly metallic gray), but the price of a Mac is just too high for me to afford or justify when a Vista laptop can be had for around $500 brand new. I really don't know how the prices run on the desktops as I don't use them. But either way, I see computers as a disposable commodity. No matter how good of a machine you get in either a Mac or PC, it will be obsolete in 2-3 years and not worth fixing. So, I always just buy a basic machine that is powerful enough to not be the bottom of the market, but not a $1500 waste of cash either ( I paid $700 for the one I have now).
To me, Apples are status and style statements while PC's are function over form machines. Both do basically the same thing, one just looks cooler doing it. Is a Macbook Air any more functional than a $500 Acer from Wal Mart? Probably not, but it sure looks cool! I will say though that I am a fan of the iPod, and own 4 of them ( 3 of which I bought broken). It's a really nice piece of art...urmm... technology. Too bad it runs off iTunes with such a strong DRM, and that they have no radio tuner. I would love to use it when I go bike riding so that I can hear some talk radio.
As for Linux, it sounds interesting and I would love to get an older, obsolete machine to experiment on and try loading it with Linux. I am curious just how good ( or bad) a free OS could be. I just don't want to try it first on my good computers and risk ruining them.