Users generally don't want to learn new abstractions unless they provide a massive benefit or can be mapped onto something they already understand. With Circle

Users generally don't want to learn new abstractions unless they provide a massive benefit or can be mapped onto something they already understand. With Circles, Google is touching right at heart of human social interaction: You show different sides of your personality to different groups of people. With your parents, you talk incessantly about the grandkids. With your buddies, you talk about old times and shared hobbies. With your colleagues, you talk about your industry. You occasionally mix things up a tiny bit, but you don't go overboard. I'm convinced that 99% of the human race gets this. (The other 1% are intolerable bores.) Now, I'm not convinced Google has nailed the UI for Circles. For example, if you want to know who can read your comments on somebody else's post, you need to click on little blue "Limited" link, and try to make out the profile photos. In real life, you would just look around the room. So there's more work to be done. But I suspect that "social circles" are something that users already understand, and which they'll value.