My feelings in a nutshell.
Windows is too much aggravation on a daily basis, so I only use that for non-gaming activities when someone's willing to pay me for it.
Linux doesn't do the things I need and, as the recent shenanigans (still only kludged around, rather than fixed) on odin show, bites me in the poorly-documented arse from time to time.
Linux is great for serving Java applications and stuff like that. It's not so great for lazy bastids like me who just want to read their mail, do a little surfing, play a few games and have truly great font rendering.
It's the little things like the services; the text areas with built in grammar and spell checking; apps like Delicious Library; iTunes (yeah, some hate it. I love it.). The fact that Jobs rules the GUI with an iron fist means that you don't get the Windows Disease of every company feeling the need to reinvent the toolbox/menu/GUI to achieve "brand separation".
I've never pretended that OS X will work for everyone, but it works for me. My very first reaction to OS X, some five years ago, was "*this* is how it was supposed to be!".
I've not had any real cause to change that opinion yet.