Tumblr is 4% porn!
Tumblr is pretty much a massive collection of cat gifs, fandom content, and porn (and a few other things). In 2012, David Karp (founder and CEO) said that in June 2012 between 2-4% of the site’s traffic was porn-related. The Tumblr Community Guidelines permit adult oriented content but require that blogs which contain occasional or substantial mature content to be flagged as much.
Sexually-expicit videos are not allowed to be uploaded to the site, but videos hosted elsewhere may be embedded. Some porn bloggers actually earn money by referring traffic to adult business through referrals and widgets. Shhh...don’t tell the social justice bloggers.