Sadly I can report that I am aware of three of my friends who elected to accept the free upgrade to W10 on their machines discovered some basic things that no longer worked as they did on W7 and W8. The common factor was that the machines themselves were getting on in years - still very useful and usable, but no drivers for W10 seemed to be available for some hardware components.
In another instance, an entire office elected to go with the flow and 'upgrade' about ten machines at once. All went well in the upgrade process, but the rest of the day was spent resetting basic installation parameters back to "Australian" regional settings, and trying to discover where everything they used in the past was now hiding. I think all is now well, but none of these people apparently had sufficient 'geekness' to deal with changes which they didn't anticipate or expect.
I think I'll wait a bit longer.
FOR