The Facebook Data Team analyzed the social connections between users.
We found that six degrees actually overstates the number of links between typical pairs of users: While 99.6% of all pairs of users are connected by paths with 5 degrees (6 hops), 92% are connected by only four degrees (5 hops)
Even more interesting? That distance is decreasing:
The average distance in 2008 was 5.28 hops (4.28 degrees), while now it is 4.74 (3.74 degrees?)