Tumblr has been searching for a way to earn a profit off of its ever growing userbase for a while, and now the company has announced that advertising will join its recently launched post highlighting service as a revenue source. The ads will be featured on Tumblr's Radar — a small box on the dashboard that's currently used to highlight interesting and popular posts — which CEO David Karp says will give advertisers 120 million impressions each day. Karp had previously said that Tumblr was "pretty opposed to advertising," and as recently as April 12th told Ad Age that it was "a complete last resort." In an apparent change of heart he admitted during the announcement that he was an "idiot" for making those comments. The ads will start running on May 2nd, and Tumblr has already lined up around 15 partners, which include The Cartoon Network.