At my workplace, it's about 40% Windows, 40% MacOS, and 20% Linux. Those who use Windows generally use it to ssh and/or VNC into our general-purpose Linux compute servers.

I personally have a Linux desktop as my main machine and a Linux netbook as my portable. I could see Google going the same way with its own employees, since the only things my netbook has to do is connect to the vpn and ssh to my desktop, where I connect to my existing screen session and keep going right where I left off. A Chromebook could do that sort of thing relatively easily.