In a 2010 interview with the Los Angeles Times, Tumblr CEO and founder David Karp said, “We’re pretty opposed to advertising. It really turns our stomachs.”

How times have changed. Karp announced at Ad Age’s Digital Conference that on May 2, Tumblr will start offering advertisers the ability to buy an ad unit on Tumblr Radar, which highlights the site’s top posts and gets approximately 120,000 impressions a day.

That’s why your blog is better off on an owned blog. How long will it take them to put ads on Tumblr blogs? There is no such thing as free hosting.