The main selling feature of Google+ is Circles, which controls what posts are seen by whom. Certainly, you have different audiences for different kinds of content. But, we've seen versions of Circles before.
Starting with Orkut
And there was Google Wave.
Then going to Google Buzz.
Compared to the latest iteration, Google+ Circles.
Ultimately, I don't think Google has invented anything new here. But, they may have made using groups drop dead easy; which may make all the difference. Currently, segmenting your posts is easy for somebody like me. However, it may not be easy enough for the average user.
Segmenting my posts to groups has not really been useful for me mainly because Google products have not had the same draw for other people in my life as other sites have.
For the handful of Orkut friends who still visit my profile, it's not worth breaking up posts for one or two people. My Google Buzz has a bigger group of friends; but, they are mainly people with whom public posts are fine. Not enough of my close circles are knowingly as into Google as I, so they don't check their Buzz streams. Even when I @ them privately, they don't reply.
Google's problem has not been the sharing; Google is great about sharing. The problem has been making the products appealing and easy to use. From what I see from the outside, not having an invite yet, Google has made G+ super-easy to use and visually appealing. I hope that this is enough to convince my circles of friends to give it a whirl. Otherwise, what's the point?