Because Windows 8 uses an email sign in/cloud profile, do they have access to view my data and what I am doing with it? I am always wary that one of the EULAs is signing away the rights to my soul (or at least my data).
I think your question should be "Would they do this?", because every software vendor can monitor user data with or without their users notice. Windows has full access to all resources of a computer so it's very capable of monitoring its activity and data. Add an online account to that so it can easily identify you on any device you sign in.
The point here is they must do it (if they're after it) with real care and don't mess things up for unimportant cases. If it becomes clear that they monitor and gather user data it creates a global crisis and nobody will use their products anymore and they certainly don't want this. So they could do it but they won't do it in such a way that everybody feel unsafe and worries about their data.
To sum it up if you are not a criminal, undercover agent, spy and so on you shouldn't worry about that because you are not a target. But if you are so worried about your data then you shouldn't use (I mean trust) Windows in first place. You decide how important your data is, you won't use a 800$ lock for a 100$ bike, will you?