I would argue linux is deserving of a place among that list (despite the many distributions I will lump it together). Maybe BSD and some of the others would fall under other but linux still makes that list in my estimation.
Anyhow whatever does the job I need it to do is what I use and what I install for clients- typically this means a version of XP (still a corporate standard and a bit cheaper/more commonly existing than corporate grade 7), a version of XBMC (people really seem to have got into media players of late), a version of debian (servers and such although I have been meaning to look at centOS more) or linux mint (desktops) or a version of opensuse (mainly as it winds into selinux well- people wanting secure laptops and such for banking and travelling). Outside of those that like toys, are lovingly referred to as the coloured pencil departments and/or stuff like ipads (they do have nice email and a halfway acceptable browser) though nobody has really gone for apple- if you are going to lump yourself with incompatible software or just need an OS that does a browser and VNC/RDP you might as well get one you do not have to pay for (both in software and limited selection of hardware).
After this it seems even I have got roped into virtualisation (next step- evaluating proxmox for corporate use) which makes this even more meaningless/goes towards reducing OS to an application/library/API level which for my money can not happen soon enough.
Windows 7 (64bit) at home (for gaming and developing in .net).
Mac OS X 10.5.8 at work (because that's what they use here).
Ubuntu 11.10 on my laptop (because it's an old laptop, and ubuntu is pretty lightweight).
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