Considering that Twitter did not offer advertising until it was nearly 4 years old, the company has ramped up its ad business quite rapidly since April 2010. By the end of 2010, Twitter had partnered with 150 companies for advertising campaigns on the site, said Dick Costolo's presentation at the All Things Digital D9 conference in June. By June 2011, Costolo said that number had jumped to 600. The question is: Have these experimental campaigns been successful? In researching a new report, eMarketer came across several marketers - including Asian OTA Zuji - who have shown results, though not necessarily tied directly to dollars. Get the full story at Advertising Age