“Five-year-old Tumblr has raised $125 million in financing, $85 million of which came last fall. In the last year, the site has exploded. There are now 53 million blogs on Tumblr, with a total of about 17 billion global monthly page views. The company has gone from fewer than 20 employees in 2010 to more than 100 now. They are building an editorial product, staffed by veterans of BlackBook and Newsweek, that will cover happenings inside the Tumblr community. Major brands are increasingly establishing a presence on the site, as are celebrities, media outlets, your friends, and their pets. The Tumblr terrarium is vast and increasingly self-contained: you could never leave the site and still live a pretty full creative and commercial life online.