Mac... I'm too poor ( well I type this on my iPhone)
I loath macs personally. Overpriced hardware (I could build that mac for half the price!) with an OS of questionable support.
Linux is for geeks
Studies show that 99% of people are geeks at heart.
I personally prefer windows, but nothing beats a dual boot. Who said you can't have your cake and eat it too (catering services excluded).
Granted, the UI of Vista/7 seems to be a big issue for many, but personally, I think that any major change like that will merely take a long time to get used to, but once you get used to it, it will be hard to go back, and you'll know exactly where everything is. For example, when the school computers upgraded to Office 2007 (and later 2010), I was very lost and confused for the first few weeks, but now I'm so used to it I can hardly remember how 2003 was (all I know is that it's similar-ish to OpenOffice.org, which I use on my home computer). Likewise, the vista UI and folder structure took some getting used to, but now XP feels alien and let's not talk about windows 95 (I kinda skipped over 97 and ME, going from 95 to XP. Kinda a mind jolt). The bottom line: All major changes are controversial at first, but everyone get's used to it eventually. I could continue this topic into many other non-OS related changes that went from controversial to universally accepted, but that would probably end poorly.