I'm still running XP on my desktop. It's sort of like a super-secure storage box since it's never even seen "The 'Net" and it's got a 3 - 1/2" floppy drive on it. I run Win7 on my HP laptop.
In a way, excepting for genuine tech advances (like bit width) an operating system is just an operating system, and newer "versions:" just have different software hung onto it. In a way.
Most of the original DOS commands are still available, with different and newer switches. After all, dir C: still gives you a dir C, and dir C:/p still gives you a dir C a page at a time.
So it may be naïve, but looking at it that way keeps me comfortable about keeping old systems around,.