Twitter has completed its 300 millionth user registration, meaning its census nearly matches that of the entire United States. It's economic output, not so much.
Twopcharts.com tallies just over 301 million Twitter registrations, not far behind the 308 million Americans in the last census. Sadly, many of those Twitter people are inactive zombies, or mute. And even the 21 million or so who are active aren't making very much money for the company; Twitter's revenue was reportedly just $45 million last year, a tiny fraction of its more than $1.5 billion in venture funding, to say nothing of competitor Facebook's reported $2 billion in 2010 revenue. Of course, as Business Insider points out, Twitter is trying to fix all that—by hiring Jack Dorsey as a product designer, part time. Good luck with that.