I use Linux mostly but log into OS X or Windows for those. I could probably run them in a virtual machine though.

The one thing that keeps me from using Linux exclusively are pieces of software that I use to make music but are only available on Windows (e.g. Guitar Amp Plugins by LePou or various processors by Variety Of Sound). I don't see those coming to Linux anytime soon, sadly.

If Reaper would come out in a native version for Linux and someone invented a way to use Windows VST plugins in it without a performance hit, I might dare switching.