A while ago we participated in an on-line project to test the small world hypothesis -- the idea that people are connected by only six degrees of separation.

Some of the results from that project have been published in the journal Science.  You can download a copy of the results here, http://smallworld.columbia.edu/results.html and also examine the methodology.

This study has some interesting implications, not just about "social connectedness" but how one can use the internet and, Gasp!, "self-selecting respondents" to do what seems to be valid social science research, at least of a specific sort.