John Tierney, science writer at the NYT (and my very favorite NYT writer) suggests in this piece that the kind of things most likely to be shared with others through e-mailing tend to be "articles with with positive rather than negative themes, and they liked to send long articles on intellectually challenging topics." Perhaps most surprisingly, readers like to share an inordinate number of science article, especially those that inspired awe or were on large-scale topics or had to do with surprising research results.
How does anybody know? Researchers at the University of Pennsylvania checked the NYT's list of most-e-mailed articles every 15 minutes or so for more than six months and did their best to correct for placement in the paper or on the Web page. They had expected articles with practical tips to be most prominent, or maybe stuff about sex. But they found science articles disproportionately predominant, and not the practical applied-science stuff but the pathbreaking eye-opening, mind-expanding stuff, stuff that invites you to see the world in a different way, on things like paleontology and cosmology.
Maybe there's hope for humankind after all.