The European Network and Information Security Agency (ENISA) has just published a comprehensive position paper on Web 2.0 Security and Privacy. It's a good overview of the problem and solution space, and a useful reference document for all information security practitioners.
ENISA also conducted a survey of 1,500 end-users of Web 2.0 sites and applications. The results of that are also worth reading, though I'm not sure that the reported differences in user behaviour between countries are really as large as they appear from the survey, perhaps reflecting differences in the targeted audiences.
