Problem is, what happens when they stop supporting the version that you are using and happy with?
Would you feel confident going online with an OS that has known security issues that will never be patched?
Would you feel confident going online with an OS that has known security issues that will never be patched?
1/ Put the computer behind a NAT router with no open ports/outside access 2/ Use a browser that hasn't dropped your platform (just because the OS isn't supported anymore doesn't mean you can't find at least one browser that's up to date with continuous security updates. There are still people porting Firefox to PPC macs, an initiative called "TenFourFox". You can also try Camino or iCab, two alternative browsers that have kept PPC compatibility) 3/ Don't open an email attachment unless it has been scanned through an antivirus
Point 1 and 3 are something I do even on a patched computer anyway. Your desktop shouldn't be directly exposed to the internet.
I've never ran an outdated OS myself but I would feel confident in using one as long as I respect those principles. The one thing I wouldn't be confident in doing, though, would be running an outdated browser or an outdated mail client. Security updates for anything that is in direct contact with the internet is a top priority and using an abandoned mail client like sparrow that doesn't guarantee security updates is a terrible, terrible idea.