Facebook doesn't allow your status updates to be public.
steer was asking how the circles system in G+ was different to Facebook's friends list system. And the difference is that it's more like LJ's friends lists than Facebook's. Which is to say that, like Twitter, you can 'follow' anyone, even if they don't want to be followed. And like LJ you can post to a particular circle, a mixture of different circles, all of your circles (the equivalent of friends-only) or make a post public.
And that means that a G+ identity can be used as a public identity as well as for chatting to your friends. And this is something I've not seen on any other social network since LJ came along.
Now, if it only had threaded comments, I'd be happy!
Original post on Dreamwidth - there are comments there.