We have numerous PC's still running XP. MS seems to not see the importance of backwards compatibility. Reliability, stability, compatibility far outweigh new gadgetry and gizmos added. We have quite a bit of custom software that will not run on Windows 8. Some won't run on Windows 7/8 because of MS's dropping of MSJava when .NET was created. Rewriting all these applications in .NET would cost a fortune without any gains. Not a problem for our applications written decades ago for Unix. An easy recompile and they're up and running on modern hardware under Linux. Wish Windows was so easy and stable! Our Windows based servers tend to crash and require reboots a few times a year. Our Unix servers have been running for over 4 years without a single crash. Windows 8? Bahhhh!!
We also have several DOS PC's!! They are used to run a single custom program 24/7. They run, never crash, never need maintenance etc. Rock solid stable.