Being poly-operating-system also gives you a unique viewpoint and can be an advantage in most things, provided you're using each OS for what they are best at and not just trying to emulate a different OS.
I do all my work in Linux and when I'm coding, spend about 90% of my time in Linux, but for my most recent setup, I elected to run my Linux install in VirtualBox on a Windows 7 host and this has worked very well for me so far. I use a tiling window manager and spend most of my time in terminals anyway (vim is my editor of choice), so its not like my install requires a lot of resources - its almost like running a terminal in a fancy window. I use windows for (non-documentation) related web browsing, for using Visio, Office (since my other team members use it, I find its less trouble if I do too) and Balsamiq and, most of all, for playing games.
Very happy with this poly-OS setup.