I loved OkCupid's analysis based on data from their site, and I liked this blog post too :) .

Facebook must be absolutely fascinating for researchers, I wonder if they make anonymized datasets available for universities? - Edit: they do

https://snap.stanford.edu/data/egonets-Facebook.html

http://www.michaelzimmer.org/2011/02/15/facebook-data-of-1-2...