(Also, I'm somewhat confused by the question, as I specifically demonstrated something that is akin to a suggestion by way of demonstrating what Facebook did right... why are you asking this? There are a million ways to do "invite closed communities rather than random people", like allowing Google Apps domains to join rather than people: that way you at least could get "my company/organization circle" or something; you could imagine inviting e-mail domains, so "anyone with ucsb.edu e-mail addresses now gets on", etc.: the problem is that I now know a small handful of my friends who are using Google+, but as most of my friends can't I will rapidly tire of posting there when I can post to Facebook.)