Tumblr, the blogging network that boasts over 170 million monthly visitors, began to run ads last year for the first time – a decision that ran against the stated ethos of CEO David Karp, who once said that “[the company is] pretty opposed to advertising. It really turns our stomachs.” It now appears, however, that he has reconsidered, and Karp now maintains that creative, well-structured advertising can work with Tumblr. An example is the recent Ford Lincoln campaign that featured vintage cars and cinematography. Other potential reasons have surfaced, such as the rumored $13 million in revenues that Tumblr earns annually from advertising. With Tumblr shifting increasingly towards mobile, how they choose to advertise will be an important subject of debate, with 170 million pairs of eyes per month at stake.