A recent Ofcom report raises good questions about the appropriate default settings for social networking sites, particularly in the case of younger people. See their report:
If default settings were such as to prevent the release of data, such as birthdates or photographs, unless explicitly and purposively opened to wider audiences, they might prevent unwanted access to personal information. A recent study on the use of wireless routers supports the value of using more restrictive default settings. The study is reported in an article by Rajiv C. Shah and Christian Sandvig (2008), ‘Software Defaults as De Facto Regulation: the Case of the Wireless Internet’, Information, Communication and Society, Vol 11, No. 1, pp. 25-46.
The authors conclude that ‘defaults act as de facto regulation for the poor and poorly educated.’
The article is available online: http://papers.ssrn.com/sol3/papers.cfm?abstract_id=964950