Jack Dorsey. Twitter is celebrating its fifth anniversary! The first tweet was sent out on March 21, 2006. "just setting up my twttr," wrote @jack, a.k.a. Jack Dorsey, Twitter's creator and co-founder. Since then, Twitter has registered more than 175 million users, who have sent out more than a billion tweets. At least 400,000 people sign up for a Twitter account on any given day, according to co-creator Biz Stone. (Prime Minister Stephen Harper, Liberal Leader Michael Ignatieff, NDP Leader Jack Layton and Bloc Québécois Leader Gilles Duceppe all have Twitter accounts. So does Justin Bieber.) In 2010, Twitter users sent an average of 50 million tweets a day. In Feb. 2011 alone, the average number was 140 million. The number of employees has jumped from eight in Jan. 2008 to 400 in March 2011. "Twitter is growing at a record pace," the company says. NB: Asante sana Jack Dorsey kwa kutuletea njia mpya ya mawasiliano. M/Mungu akupe maisha marefu.