Microsoft admits Windows 10 preview has a keylogger
Microsoft has admitted that the new Windows 10 operating system tracks keystrokes and examines audio input. The new operating system, currently a free download for users with Windows 7 and Windows 8 licences, not only tracks how long it takes to open different types of files, the make and model of device you're using, but it's also logging keystrokes and collecting voice recordings. Microsoft will not delete data already collected from Windows 10 users.
So I am not afraid of whatever ugly things can be found in Windows 10. On the other hand, I need a very compelling reason to change. With my use case I could still use XP without risk. The only reason I have Windows 8.1 is that I bought a new computer a few weeks ago. :-)