Google has at last thrown Google+ open to everyone - now we can all sit around and comment how much it looks like Facebook. The initial roll-out was to selected users only (oddly enough a lot of tech journalists seemed to get hold of one) who could then invite friends so the idea is well established and it already has tens of millions of members.
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.
It's very different now - and things can change in social media too. Ask any long-established MySpace shareholder.