For the consumer market, Win10 will mainly be a case of you get the update whether you want/like it or not.
Business users will be less stuck with this option, as updating anything can potentially break s/w which in some companies could be critical to health and safety.
I'm backing up my current Win7 machines so that I can rollback to them should Win10 not be to my liking (though having been through numerous iterations of the beta testing I don't see it being an issue).
Just one XP machine to upgrade to Win7 and then that's good to go too
Now if only Nikon would do something similar.... a free upgrade of the core of their product (in this case camera body) to the latest and greatest
Happy days would be all round