Sometimes, the choice of OS comes down to the availability of tools to do your work. I work in an embedded environment with esoteric compilers and debuggers. Trying to get the vendors to support them in an OS other than Windows in impossible. So I am living in Windows land for my daily work. I use OSX at home, and I cannot really say if my productivity level would go up if the embedded tools were available under OSX.

Having said that, I have migrated to Win7 (on a Lenovo T430 with a SSD) towards the end of last year. For a office workhorse, this setup is one of most productive setup I have used in years!