The first thing I did after reading this article was to recheck my settings and confirm my privacy settings. I like that Facebook allows me to passively interact with friends and colleagues, but I do want to control what gets released.
Privacy is a huge issue and data sharing needs to be with the user's approval. Without it, we are approaching the Orwellian world of 1984. Younger people may be more relaxed about sharing themselves and their habits, but I come from a school that is more careful about being that open. Not that I have anything to be ashamed of, but that I should be the one to determine who knows what I do. I know some folks that don't even want to put their picture on their page, preferring to use an icon or nothing at all.
As long as the data is analyzed in the aggregate and not specific to the individual, than the understandings of behaviour can be useful to research. But to share ones specific purchases, reading, or viewing behaviour is something that should remain private. Let the individual determine what is to be shared and get specific approval, else be careful of the repercussions.
Social networking has allowed us great opportunities to interact and to communicate in meaningful and frivolous ways. But it comes with many pitfalls. Facebook, My Space and all other sites need to protect the individual content from unauthorized use. Any release should require specific approval. And it should be incumbant upon the site to be proactive before legal issues arise.