I'm reading a couple of interesting books right now [see my Shelfari list here] including Guarding Life's Dark Secrets: Legal and Social Controls over Reputation, Propriety, and Privacy by Lawrence Friedman of the Stanford School of Law. The book examines the legal and social norms governing privacy, reputation, sex, and morals over the past two centuries. It's worth putting on your reading list. [Here's a detailed review by Neil Richards.] I might pen a full review later but for now I thought I would just snip this passage from the concluding chapter:
In an important sense, privacy is a modern invention. Medieval people had no concept of privacy. They also had no actual privacy. Nobody was ever alone. No ordinary person had private space. Houses were tiny and crowded. Everyone was embedded in a face-to-face community. Privacy, as idea and reality, is the creation of a modern bourgeois society. Above all, it is a creation of the nineteenth century. In the twentieth century it became even more of a reality. [p. 258]
[Note: If you're interested in this topic, you'll also want to read Daniel Solove's The Future of Reputation: Gossip, Rumor, and Privacy on the Internet. Also, here's Jim Harper's review of it.]