The Forced Social Network
doubledbl.tumblr.com
doubledbl.tumblr.com
But here's a metric which doesn't exist but probably should: how much perceived value are users getting out of a service? On Google+ I can watch a live stargazing session take place complete with through the telescope views. On Facebook I can see what that douche I talked to once had for brunch.
Some of it is the interface (Google's a lot better at this stuff than FB) and some of it is the userbase (G+ seems to skew towards techies, and er, "intentional" users, rather than "everybody, and that includes uncle merl").
The question I have is if G+ manages to really get some traction, and does start to attract the unwashed masses, how will this feel change? G+'s more nuanced contact model might help a bit, but...