For a long time I've just been running Linux and use emacs and the zsh shell as the main environment I operate in within it.
I recently got a laptop though and for reasons I won't get into, have a visceral and probably irrational dislike for Apple and I really didn't want to deal with Linux wireless not working well, or sleep not working well, or whatever else may or may not work well on the laptop. Anyway, for the laptop I got a machine with Windows 7 and I installed Linux on top of it in a virtual machine.
I have to say, I love it! If I want to look at something in IE or use MS Office (I prefer it over OpenOffice, sorry), or whatever else I might want to do in Windows, I don't have to reboot. I can snapshot and tinker, without worrying about breaking it, and Win 7 works really well. When I want to do dev work I boot up the Linux VM and put it up full screen and haven't had any problems yet. Next time I put together my main machine, I'm considering doing the same there, though I have gotten quite used to all the Linux apps.