Open Digital Policy Blog.
It will take a bit of time for users to thoroughly understand the functionality - and any unintended side effects - of the new features of Google+. Already, my partner in Open Digital Julian Ranger has uncovered a potential for spam.
But my general impression is that rivals should be very worried indeed. Until yesterday there was no serious rival to Facebook. If you wanted to share a few photos and have a chinwag with friends you had Facebook or a slew of buggy functionality-void rivals.
A challenger doesn't necessarily have to beat Facebook, it just has to offer a credible alternative. There's enough reasons to leave Facebook, but I'll get on to that in a minute.
Part of the credibility challenge is providing impetus: a critical mass of initial users so enough people can try out the features; and Google is one of the few companies in a position to do that, literally overnight.
Google has keyed Google+ into its mainstay - the search page. I noticed a new top menu on Google.com a few days ago, and this is why. Google+ notifications etc will be tied to the one page most of us use with equivalent frequency to our favourite social network. Clever.
I mentioned reasons to leave Facebook. In addition to the obvious well-reported issues (privacy, privacy and an over-bearing obsession with identity and control) there's the baggage.
All the friends we added when social networks were new and our standards were eclipsed by our eagerness to play with a new toy. The hours wasted filtering our streams of the goats and potted plants bought for us by an almost-stranger we once snogged 23 years ago behind the sports hall...
A new social network gives us a fresh start. No people we haven't spoken to since that fateful fumble, plus a chance to sort and group the people we choose to add into circles.
All of a sudden the valuations for one-product companies Facebook and LinkedIN are looking incredibly optimistic.