From another newsgroup that I subscribe to.
The European Network and Information Security Agency (ENISA) has released a position paper on Web 2.0 technologies, including social networks.
http://www.enisa.europa.eu/pages/02_01_press_2008_12_10_web2.html
The document enumerates a variety of vulnerabilities in Web 2.0 technologies and discusses high-level recommendations for each. The document does seem to have an overall positive view of these technologies.
Henry, what a valuable find! Thanks for posting about it.