Privacy is an interesting concept. It means very different things than it did a decade ago. But what is it really? We've never had much privacy in our own networks (family and friends often know more than we want, if you live in a small community you sort of know what's going on). Where we did have privacy was from sources that we didn't trust. It's ok if my brother knows I like a particular product, have a certain hangup, or a particular weakness. It's not ok if a company knows that. We too often equate privacy with the notion of not being known (for example, when someone you know in the physical world mentions something they found out about you online, we can see that as "wow, I have no privacy"). But truthfully, privacy has always had gradients. I don't want my life insurance company to know my dietary habits. And I don't want colleagues to know my bank account balance. Now, with Facebook and other tools, we are self-declaring many of our interests - an absolute dream for marketers.
As Britannica Blog notes, the ability to piece together our distributed activities likely results in the most significant affront to our view of privacy. Co-workers know different things about us than our family does, our banks know different things about us than our place of worship. These segregated chunks of our identity is what we mostly define as privacy. When our segregated selves can be brought together into a whole, parts of our identity are shared with people we don't want to share. As Teemu says, big brother, in this instance, is, well, us. We are responsible for self-surveillance - through facebook, flickr, blogs, social bookmarking, twitter.