When I say data, I'm not talking about files on your PC. If Microsoft wanted those I'm betting they'd be able to get them. It's this so-called "non-personal" data that I'm talking about; the stuff they sell to advertisers who then use this data for who-knows-what. Sure, they target ads towards you but they also conduct data mining on this information that pushes it further and further towards personal information.
- Calendar details
- Snippets of what you type to improve predictions
- Mobile number if connected to Skype
- Location/Location history (allowed to be used by any app by default)
- Wifi name and password and wifi name/password of contacts
- Browsing history
- Typed/Spoken searches to Cortana
- Diagnostic/Telemetry data
It all boils down to what you consider personal or non-personal information. I consider pretty much everything there besides language and diagnostic/telemetry to be personal information and feel Microsoft shouldn't have access to it all just because I use their OS. Oh and since I refused the free upgrade I'll be paying for that OS so the excuse of "you got Windows 10 for free so we're entitled to collect and make money off this information" doesn't hold water with me.