I always thought that the *maximum* was six degrees of separation between virtually everyone. Thus, an average would lower than six degrees...and any instances of more than six degrees would be in the minority, or outliers that may simply be because not everyone is accounted for.
Of course, this also depends on what your criteria for each degree of separation. Do you have to be just facebook friends, or should you actually have had some real physical contact (i.e., being the same room together), or verbal exchange with someone, or should there actually be a meaningful relationship that associates two people along each degree of separation? We've already seen articles in /. which that demonstrated that many people add friends to their lists without really knowing who they are or ever even interacting with them. To me, that doesn't count. Also...what about famous/popular people who have 'friends' that are really just 'fans'...does that get counted?
Using the methodology described, it's up to each person to decide who out of their list of friends is the next link is to a given 'target'...but that doesn't confirm that their association with the selected 'friend' is actually a valid social linkage (e.g., someone may pick the next linkage based on popularity, but without actually having any social ties with that person). You can make some assumptions to overcome this, and the results will be interesting...but I don't think this will be conclusive if conducted in the manner described.