Quality, not quantity: the dawn of the anti-social networks

Is it possible to have too many friends? Some of Silicon Valley's finest brains think so, which is why niche networks like Path and Diaspora are springing up to allow users to share their lives more openly with a trusted inner-circle.

Facebook hasn't just pulled away from its rivals, it has rocketed into the social networking stratosphere.

With active users last officially recorded at 500 million and now thought to be more than 600 million, Facebook has become the unquestioned king of the social media sector, leaving MySpace and Bebo eating dust in its tracks.

But Facebook's dizzying rise to dominance hasn't stopped some observers wondering if it really will prove to be the last word in social networking, prompting potential rivals to look for an Achilles heel.