Yahoo! has purchased Tumblr at a particularly difficult time in the life cycle of a Web startup. The users are there, creating and reading posts, asking the company for nothing except reliable server performance—and nothing in the way of major changes. Now it falls to Yahoo to figure out how to turn that traffic into revenue, a problem that continues to bedevil pretty much every popular social-media property on the Web.
To understand the nature of that challenge, it helps to look at the content, and the traffic, that Yahoo is buying. There is the porn, obviously. To recap, approximately one in every six pages on Tumblr has some kind of adult content, according to PrivCo, a firm that tracks private companies. Tumblr has been quietly chopping down on the smut, and only one of its top 25 sites today is pornographic, according to Quantcast.