One thing that strikes me as interesting is that Facebook repeatedly states that they do not sell personal information to third parties. Yet, I've never read or heard it stated plainly that this behavior is forbidden by applications running on the Facebook platform. In fact, at one point I remember that friends applications had access to my personal information, even if I did not authorize said application. I dont' know whether that is still the case, but the idea behind it is troubling.

I would also like to follow-up that people are dissimilar enough that de-anonymizing is not that difficult. I do not know why, yet, an advertiser would want to explicitly de-anonymize its data, but it is certainly possible.