When I'm purely in a dev mode, I do. But often, I'd like to be able to jump into online games with my friends on the same PC, and the games I like to play simply work better on Windows. It's nice to have the same or equivalent tools available on Windows for when I'm already there, so I don't need to switch back to my other boot or fiddle around with a virtual machine.
Very much a hobbyist dev machine, and I primarily write video games and related tools on this machine. Some of my emulator projects are cross-platform, so I need to be able to test on Windows for those anyway; it's kind of a general purpose workhorse.
The computer I use for my day job is exclusively Linux, as I have no need for Windows software or online games there. (I'm guilty of playing Minecraft during my lunch break, but that fortunately runs quite pleasantly under Linux.)
