Google invites everyone into its Plus network
This doesn't compare with Facebook or Twitter yet of course but Google's size makes it the most likely company of the moment to add any realistic competition to the market (that said, the largest social networking companies started from nothing rather than from a strong position).
The omens didn't look good initially. Google has screwed up massively once before with its previous social network, called Buzz. It autojoined everybody with a Gmail account and the response was predominantly hostile since people felt they weren't being given the choice and worse, their contacts and details were being shared without their consent.
The controlled release of the new offering suggests the company has learned a great deal in the intervening year and a half. And the shape of the network, in which you can put public updates up and share them but also invite people into 'circles' and offer limited updates, means members have a far greater control over their networks than they had with the scattergun approach of Twitter and Facebook.
But is it too late? Has the social media market settled on a few leaders and it's pretty much closed? That's the way it looks at the moment, but when I started as a tech journalist it looked very much as though WordPerfect would always control the market for word processing and Novell would own networking operating systems forever.
It's very different now - and things can change in social media too. Ask any long-established MySpace shareholder.