I agree that it makes sense - then again so do group security policies under Windows. And managing Circles will appeal to pretty much the same set of people who would find an afternoon of setting security policies appealing.
Circles are just not something which is going to cause a quarter of a billion people to switch away from Facebook - particularly given Google+ is invitation only. And even if that many people switched, Google+ would be half the current size of Facebook.
When I first signed into it, I thought that's how it would be, but what I've found is that as people added me, and I get the notification, I just add them to appropriate circles then.
Circles are just not something which is going to cause a quarter of a billion people to switch away from Facebook - particularly given Google+ is invitation only. And even if that many people switched, Google+ would be half the current size of Facebook.