There is awful lot of FUD in here about Microsoft. (Fear, Uncertainty and Doubt). The privacy crap is way overblown by people that don't understand it and frankly make things up and it get's worse with each telling. If you use ANYTHING from Google, you're already much worse off than the 'express settings' from Microsoft and Windows 10. In fact, the number of privacy options in windows 10 is mind boggling. But they are there and you can choose to control your privacy however you'd like. Try that with Google sometime, eh?
I was running the preview on my 7 year old laptop... no problems there. I've upgraded my other laptop, my daily use desktop, my mother's laptops. and I've only had one issue. And that issue wasn't MS, it was Dell.
Now, for those of you that have switched to Windows 10 and are concerned about the Privacy settings, here is a pretty good guide from an honest broker: https://www.thurrott.com/windows/windows-10/5337/windows-10-tip-understand-and-configure-privacy-settings
That guide covers if you are in the upgrade process or after you've upgraded. So, if you're worried, take a deep breath and go through that guide
Overall, I'm very happy with Windows 10. I love the notification center, Cortana (whom I'm always asking about the weather) and Edge is a damn good start of a browser. it's more than usable though.