Twitter has just passed the 500 million user mark, as predicted back in January, just shy of its sixth birthday. It has achieved amazing growth over the last year or so as it has become an indispensable feature of the media and entertainment landscape around the world.

There have been a lot of Twitter landmarks along the way stretching back to the 2008 presidential election through to the Arab Spring and the death of Osama Bin Laden.

Twopcharts reported the 500 million figure a few minutes ago and now predicts it will hit 600 million users in around 108 days.

Most recently we have seen Twitter turn its attention to brands as it launched enhanced brand pages and expanded its offer to advertisers with its self service ad programme.

As with 2008 we have these past few months seen how the Obama team is again using Twitter as a key part of its election campaign in what is being called the 2012 Twitter election.

We’ve seen the launch of Twitter for News highlighting that close relationship with the media, where big stories like the death of Whitney Houston continue to break first.

The growth of Twitter is also truly global. Beyond the US and UK growth has been spurred in places like Brazil, which is has become the second biggest country on Twitter .

We’ve also seen how it has become a consumer social media power house as Twitter brought LA Fitness to heel after appalling behaviour by the gym chain was highlighted.

We’ve even seen how Twitter has allowed former bad boy Joey Barton a PR makeover

What other Twitter moments stand out for you?

Graph via Raak Digital