It started out as the coolest new thing for college kids. Now Facebook's global campus comprises more than 900 million users in 70 languages.

"Leaps and bounds doesn't even describe how much this company has grown," says social media analyst Brian Solis of the Altimeter Group in Silicon Valley. "It surely has eclipsed anyone's predictions."

Andy Smith, the author of The Dragonfly Effect - Powerful Ways to Use Social Media for Social Change, says Facebook's current pre-eminence was far from inevitable.

Facebook won out with its astute sense of what people wanted to share online - photos, games, status updates and tagging friends in picture albums.

Solis says "Facebook became this great epicentre that had momentum, opened its doors to the world and the world responded".

The response took very unexpected turns. Facebook became an enabler of social change.

US President Barack Obama's campaign tapped into the network to help win the White House.

Facebook was used to spread information, circumvent censorship and co-ordinate protests during the Arab Spring. 

"Social technology did not create the revolution. Social technology was the rails on which it ran," Smith says.

'Digital Darwinism'

Now, Facebook is about to join internet giants like Apple, Google, and Microsoft as a publicly traded company. It's estimated that when the company debuts on the Nasqdaq exchange this week, it will be valued at $100bn or more.

The change will be a new business environment for Mark Zuckerberg, the 28-year-old, T-shirt- and hoodie-wearing Facebook founder and CEO.

As a publicly traded corporation Facebook will be required to disclose much more about its business deals and submit to more government oversight.

"Everything of material impact or potential material impact has to be reported including things like small suits about privacy or investigations by the government," Smith says.

Facebook, while wildly successful, is far from perfect. Its privacy policies have been criticised for over-sharing personal information.

This week General Motors decided that putting its advertisements on Facebook was no longer worth the $10m it spent last year, and pulled its advertisements. Upstarts like Pinterest could erode its member base.

What could be most disturbing for Facebook's continued growth is that, now that it has been so widely adopted, it is no longer as attractive to the young subscribers who drove it to the top.

Many Instagram users were dismayed when Zuckerberg bought the hip new photo-sharing app for $1bn - not because ot the jaw-dropping price, but because they worried Facebook might ruin a quirky and beloved social web application.

"In an era of digital Darwinism you have to compete for relevance in real time, almost faster than real time," Solis says.

In other words, Facebook will only stay successful if it stays cool.