It's always struck me that if an OS is stable enough that a support line is no longer profitable far from being the time to stop using it that's the time to start using it!
I'm with Steve on this. My rule of thumb centers on the fact that Microsoft has blown every other release of the Windows O/S badly. I will not upgrade to the next "good" release for at least a year after release, and preferably not until Service Pack 1 has been released AND a year has passed. While I don't mind being on the leading edge, I prefer not being on the bleeding edge.
I'm being equally circumspect, registered for it but I'll stick with my franken8.1 for at least a year.
8.1 with classic shell in full XP mode, file explorer in XP mode, start and metro/modern fully disabled, charms disabled, gestures disabled, all apps disabled, uninstalled, unstaged and deleted! UAC fully disabled. Then all the options Shane mentions switched off and IE disabled.
Finally override trusted installer throughout the filesystem and registry, so when you're admin there's no mysterious higher power controlling your machine. And at last 8.1 is usuable. (that doesn't mean running as admin - but I don't see why my own machine should tell me even when I explicitly promote to admin that I can't delete an old file!!!)
From what I've seen 10 is just as bad and superficially very similar, if not in some ways underneath worse; I can't see MS not wringing every last drop of personal data out to compensate them for the loss of revenue. They are moving to a google model which says all your data is our data and 10 is the vehicle. Android and OSX / iOS have been using that model for years now one openly the other behind the curtain.