Your exposure on social networks can enable a rather unusual solution for general computing applications.
For example, a future computer system may question you about who you know and who you do not and grant you access to the system based on your answers.
Yahoo has filed a patent application based on this idea and calls the technology "non-textual security using portraits." In effect, the system could take some pictures of your Facebook friends and then add some random pictures of those who you do not know. You will have to indicate which people you know and may be asked to state their names. The system could expect you to know the names of those who are social network friends and determine those that were randomly thrown into the mix, but Yahoo explicitly states that this technology would be applied when users cannot or do not want to enter text.
We have some doubt that this security approach can ever make it into a real-world implementation. Those with only three friends are screwed right off the bat and an easy target for hackers. Those who are on a mission to outfriend their peers and claim to have thousands of friends on Facebook may be completely locked out of their account when they can't remember all those pictures. Of course, we also have to hope others don't post anything else other than their face as a profile picture.