Excerpt from an extensive Andy Hertzfeld interview
I'll come back to Circles in a second, but can you just give me kind of a high-level view of what G+ is? What was the intent for Google+, and what are you hoping to do with it?
Hertzfeld: Sure. Everything on the Web can be improved by knowledge of your social connections, so Google+ is an effort to...add a social layer to Google, to YouTube, to Google Search, to every Google property. And so the core of Google+ are some APIs and applications that let you organize [and] maintain your identity through a profile and organize the people you know. Really, one of the main contributions we're making compared to the status quo is giving you much finer grain control over your sharing. You know, instead of just having an undifferentiated mass of people, we make it really easy and at the forefront of the UI to send some things to some people, other things to others.