Facebook has just announced that it has reached the amazing 500 million user milestone, leaving all competitors in its proverbial dust.

This half a billion figure is even more impressive when you consider that, unlike Twitter, a great deal of Facebook's users spend an awful lot of time on the site, with retention being high and therefore making it a very appealing prospect for advertisers.

As Zuckerberg puts it:

"I could have never imagined all of the ways people would use Facebook when we were getting started 6 years ago".

"I want to thank you for being part of making Facebook what it is today and for spreading it around the world".

As previously reported Facebook will be running user driven "Facebook stories" to "announce and celebrate" the milestone, touching on experiences such as “finding love”, “coping with grief” and “natural disasters” - adding a little meat to the half a billion bone - and has put together a photo album with "its messages of thanks".

Despite the criticisms levelled at the social media behemoth, such as concerns over privacy, child protection and just the sheer size of the organisation, Facebook has continued to grow and looks to be changing the web for all of us.

Let us know your thoughts on Facebook's milestone in the comments below. Will you be celebrating? Or are you becoming more concerned with the size of the social network?