Facebook Dominates Social Referrals

It's not surprising that Facebook dominates the social referral market. With more than 20% of  total social media traffic referrals as defined by a survey by Shareaholic, it still generates more than 4x the number that Pinterest, the market's number 2, does. The interesting thing to note is the dropoff after Facebook and Pinterest. Twitter does not even account for 1% of total social media traffic referrals, a surprising thought. Moreover, the top eight, which include other well known names such as LinkedIn and Google+, collectively account for less than 30%, leaving the rest to the long tail of other properties. My question is, who are those other properties? 70% is a big number. Is there a theme or sector that, despite being separate from a domain standpoint, share a common interest or user base? If so, maybe marketers that thrive on virality may have an untapped opportunity somewhere within the 70% of social network referrals outside of the big 8.