I've always thought that in the venture capital business you either want to be very early or very late but not in the middle. I've also thought you either want to be a boutique with a few investors or an institution with many, but never in the middle with the bureaucracy of an institution but without the scale.
And I think privacy is like that. You either want to be totally public or totally private, but never sort of private and sort of public. It's just too complicated to be semi-private. That middle ground is treacherous.
If you look at the Foursquare checkin screen:
You see that Foursquare is going to send the checkin to your "friends". That is the private channel where you've hand selected who is going to see that checkin. But you also have the option to send the checkin to Twitter and Facebook. Those are the public channels where your checkin is going to be seen by everyone.
The problem Facebook is having right now is that they are sort of private and sort of public. I think of them as a public channel. I don't post anything to Facebook that I don't want everyone to see. But that is not how many of their users see them. I believe Facebook is going to have to choose to be either totally public or totally private or they are going to gradually cede their social graph to services that stake out the totally public or totally private territory.
Privacy is pretty black and white. It either is or it isn't. And trying to have it both ways won't work.