Re: for whatever reason are still running Windows Vista...
Sorry but I dont' see Windows 10 as requiring retraining, you can make it look like Windows 7 pretty damn easily and without any third party stuff. At most you'll need a one page showing the different ways to shutdown the PC.
It's less of a problem than when moving from some versions of office, such as 97 to 2007 etc. That really messed with admin staffs head. Ribbon? Ribbon can fuck off was their motto.
The bashing on Windows 10 is getting juvenile, the focus should be on the privacy/cloud aspect not the interface - which frankly is not absolutely fine.
I realise I'll be downvoted, feel free, I'm no fanboy - I use Linux at home but the Windows bashing is simply bandwagon jumping these days.