Ripples is a new visualization feature of Google+ which shows the propagation of posts across different users. Circles within circles indicate resharing. The easiest way to see this is to go into your Google+ stream, select “What’s Hot” from the list on the left, then click on the little arrow in the right hand corner of any post and select “view ripples”. You can click on a timeline at the bottom and watch the post spread, and also see some summary stats about influencers. (and yes, none of my friends are using Google+ much either, which is why this only looks good on public “what’s hot” posts)