Amazon is often considered a lumbering giant, so it's great to see this type of innovation from them. We all know they spend lots of time on UX, but I had no idea they had teams thinking outside the box like this.
That never really took off in Google Groups, but that didn't really have the social structure around it that Google+ does. I wonder if the second time's a charm for them.
And, Feynman had a gift at making these ideas accessible to the layperson. He is very missed.