If you accept the Terms - which you must - then you have accepted that Microsoft can pretty much keylog everything you do.
Microsoft wants to track you online and collect data about your computing habits.
Microsoft is not deceiving anyone here - they are open about it. All you have to do is to actually read what you accept. Redmond has this to say about it:
With Windows 10, we're kicking off the largest ever open collaborative development effort that will change the way we build and deliver Windows,
And in order to achieve that they need to monitor you:
Users who join the Windows Insider Program and opt-in to the Windows 10 Technical Preview are choosing to provide data and feedback that will help shape the best Windows experience for our customers.
To be specific:
Redmond reserves the right to collect such info as, "your name, email address, preferences and interests; browsing, search and file history; phone call and SMS data; device configuration and sensor data; and application usage."
So to sum it up:
You help Microsoft make the best Windows ever... for that you will spill your guts and sacrifice privacy and probably not be able to downgrade the Windows you needed to install the tech preview on - but you will get the pleasure of paying full price for the end result.
Which will be a much better Windows - thanks to you.
Deals like that don't come along every day... Jump on it - be a part of it - or .... don't
More here