Mine, not yours! Global notions of privacy and ownership

I know that there are vastly different notions of privacy and ownership in different parts of the world, and was hoping that you could share your opinions about that.

So if, for example, a friend comes to your place, starts looking around on your desk (and I mean really looking, lifting up papers or files to see what's underneath), sees something of interest and picks it up to read it, do you feel that that is an invasion of your privacy?

How about if someone uses your computer and opens up all the files on your desktop, just out of curiosity?

What if someone just takes something of yours, because you have two and s/he has none?

How do you react? Does it depend on what kind of relationship you have with the person? Is it different if it's your spouse, or a friend, or someone you're dating? What's up with that?