It's pretty hard to find a site on the internet these days without some sort of advertising. The larger the site, the more it costs to run and the more income the site needs to have. Tumblr receives and incredible 4.5 billion impressions each week which makes it one of the internet's biggest destinations.
Incredibly, Tumblr has zero ads on it and they plan to keep it that way. Hosting servers for 4.5 billion impressions a week isn't cheap, so the company is trying to find a way to make money and become self-sufficient. Right now they are simply running on investment dollars, something that can't go on forever.
CEO David Carp has said in an interview that the site does not want ads. He says that Tumblr is "selling our desks to avoid that, it's a complete last resort." That's some dedication to keeping the site ad free, but can it really work? Karp and Tumblr are hiring a professional revenue executive to help monetize the site.
They have started selling highlighted posts for $1, which is basically a form of advertising, but not in the traditional sense. I really hope Tumblr can come up with an ad-free model that can then be copied by other sites across the web. I'm sick of being the 1 millionth visitor to every site I visit.