How much of your personal life is on Facebook, MySpace, blogs, Flickr, or YouTube? Are there things you would like to share with some people, but not everyone?
We propose that users protect semi-private personal content on the Internet behind questions of shared knowledge. For instance, "What is cousin Rodney's catchphrase?" can allow access from a hundred extended family members without giving them accounts, passwords, and tediously adding them to access control lists.
See also friendbo.com.