Way to make an OS poll and list only Windows lol.
My primary OS is Linux (currently using Ubuntu and Gentoo). I'm running Windows 7 on my tablet, only because of the lack of tablet integration available currently under Linux (I'd kind of like to help change that, but we'll see).
I've also worked a bit with Solaris and FreeBSD (I actually have my own dev branch in their kernel... but I stopped that a few years back) but mainly for development purposes. The main thing that stops me from using *BSD as a desktop OS is GFX card driver support. I don't really want all my stuff running in VESA modes all the time

. I suspect I'll be developing mostly on RHEL at the new job

.
I also have this thing for NetBSD. I just think it's really cool. Though, haven't used it for anything too big, nor really developed much for it.