The national privacy watchdogs (often administrative authorities) produced a report on privacy and social networking. They are particularly concerned about the level of disclosure and the lack of prior consent of all parties involved, whether what is disclosed are pictures, details of life in writing or videos. They recommend that whoever posts information, notably pictures, obtains prior consent of people involved or face exclusion from the social network.
Given that the basis of those networks is to share information, often without consent, the recommendation would be a blow to those technologies. I personally think it is not the way forward; rather, we should differentiate between those participating in the network and those not participating. Those in, by the fact of subscribing, should have a opt-out; those not in should have an opt-in.
More sensible is the recommendation that social networks warn clearly and extensively at the level of disclosure faced by their users and how that information could be used against them or their family and friends.
See the summary on Euractiv
For the report itself, Article 29 Data Protection Working Party
It is worth comparing with the 2007 report from ENISA, the rather silent EU agency on cyber issues, Enisa Position Paper EU agency for network and information security suggests updating legislation to face new social networking-related risks (25 October 2007)