I have a Windows XP system, but it is "off the grid" and will remain so. I expect it to work essentially indefinitely(especially since I have a big cache of replacement hardware), and security updates are not a concern for a computer that never connects to the internet. I have a lot of software on that computer that will not run-or at least will not run well-on newer versions of Windows.
My main computer these days is a 13" Macbook Pro. I bought this computer before Windows 8 was released, but seeing the disaster it has become, I'm not sorry that I made the switch.
I also recently picked up a Powermac G5 for $100. As Macs go, this is a "dead end" as Apple quit making Power-PC based Macs about 8 years ago. I'm stuck at OS X 10.5 with it(the current version is 10.9). Even so, it's still a fast, powerful, and very useable computer. As a bonus, I really doubt there is anyone out there writing virus for Power PC Macs.