The W3C report mentioned in the previous post says that, "Privacy means giving people control over their data, empowering people so they can communicate the way they want."
The Diaspora Project, described in the New York Times, is one response to the issue of privacy.
There also is an interesting post by skyfire on hubpages that goes into privacy on Diaspora. You are allowed to do things such as deleting or downloading your data, controlling who comments on your posts, and preventing yourself from showing up in search results, amongst other things. Unlike other social networks, Diaspora does not have advertising. This means data is not harvested for advertising (nor is it harvested for any purpose). Interestingly, Diaspora is also decentralized, which provides a means, perhaps fundamental, to preserving privacy. Yes, it seems so. Please see Eben Moglen's Freedom in the Cloud talk, which inspired Diaspora.