Love the notion of "Dark Social" as a web traffic driver. So true!
What a fantastic post by +Alexis C. Madrigal
about "Dark Social." This certainly matches my experience. And another dimension - even things that may appear as links from Facebook and Twitter may have first emerged from email and other "dark social" networks. I'm sure I'm not the only one who gets a great link from a friend via email and then shares it out over Twitter, G+, or Facebook.
And all these things might overlap. For example, I saw links to this piece go by on twitter, but there was never enough context for me to follow the link. But when someone sent it to me in email, with a bit more context, I followed the link, read the story, and reshared it here (and will do the same on Twitter.)*