On March 21, 2006, Twitter was launched, and "inviting coworkers" was the first tweet sent out by the company's co-founder.
Since then, Twitter has grown to more than 175 million registered users. According to the site's official blog, people post a billion tweets per week.
Just last week, Twitter says it set a record of 6,939 tweets per second immediately after the 9.0 earthquake struck Japan, and 177 million tweets went out as the day wore on.
The site now averages 140 million tweets a day.