I know "Post-PC" is the more popular buzzword, but "Post-OS" is probably a good one to use.

So much stuff is in the cloud these days that a lot of non-developers and non-creatives can probably use any OS these days without too much pain.

I switched to Windows from Mac a couple of years ago, and honestly, I don't miss it much. I did have to write off a pile of Mac software purchases, but I found reasonably priced alternatives that work as well.

If I get sick of Windows, I can easily transition to something else. Outside of some platform specific games, I can do just about everything I do now on another OS.