On the March 21, 2006, Jack Dorsey sent the first public tweet into the world ("just setting up my twttr"). Can you believe that was six years ago today?

Dorsey was evidently one of the key people in the early days of Twitter, and today he still serves as the company's executive chairman and product lead, combining the job with his role as CEO of Square (another company he co-founded).

His 'twttr' tweet was the first of several billions and counting.

Fun facts: it took Twitter three years, two months and one day to reach the first billion tweets, and it took about 18 months for the first 500,000 users to sign up.

Twitter-the-company has obviously come a long way since Dorsey published the first tweet on 'Twttr,' as it was known back then, and today some estimate that 500 million people use its real-time information and social networking service today.

Last time Twitter itself shared the number of registered users for the service was in April 2011, when they announced that more than 200 million people had signed up.

Twitter says 'more than' 100 million users were active in 2011. That number is most certainly higher today, but it's been a while since Twitter has provided updated numbers.

Last October, Twitter did say they were seeing 250 million tweets per day, a number that's likely also higher presently.

The service still sees massive spikes from big 'watercooler' events like the Super Bowl, the Grammys and Super Tuesday.

Over the years, Twitter has matured and made an impact in the areas of politics, sports, media, and more. But what about, you know, making money from it?

According to eMarketer, Twitter's advertising revenue will triple by 2014, hitting over $540 million (up from an estimated $260 million this year).

Recently, the company has been paying close attention to the different ways it can derive revenues from all those tweeters. Twitter has also recently addedmore languages and acquired blogging software maker Posterous.

However, with rising headcount costs (over 900 employees today, up from about 400 last year) and costly infrastructure and operations, the company is still reportedly losing a ton of money after its first 6 years in business.

But today, we raise our glasses to Twitter and wish them a very happy birthday.

This story originally appeared on The Next Web.

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