Obama, tweeter-in-chief?

Can any world leader rival Barack Obama's popularity on Twitter? With more than 17 million followers, @BarackObama is by far the most watched of the 264 accounts surveyed in "Twiplomacy," a study of Twitter usage by heads of government, published by public relations firm Burson-Marsteller on Thursday.

Obama was the first head of state to sign up on the social media service and the PR firm said he sent the most popular tweet of any world leader, which read: "Same-sex couples should be able to get married." His popularity ranks him fifth in the entire Twitterverse, just behind @britneyspears, according to the study.