Controversy over the first tweet does exist. Many report this as the first tweet by Dorsey but note that this time stamp is 12 minutes later than previous one.
Some more amazing stats: 572,000 Twitter accounts were created on March 12, 2011 alone. The number of mobile accounts has increased by 182 percent in the past year. The record of tweets per second is 6,939 set in Japan, 4 seconds after midnight on New Year's Day.