I've put together a custom google search for social networking related searches, it can be found here:
http://www.google.com/cse/home?cx=013791148858571516042:ntbykhk-kus
This can provide an idea of what an individual's social networking footprint looks like.
Examples of the sites on the list include:
facebook.com
flickr.com
plus.google.com
I will be constantly updating the search engine.