This is actually a feature of the Commons about which I'm most pleased. firstly, rating contributions gives people a way to engage when they don't want to add a contribution. And it's a great way to find out what ideas resonate with people. The problem with most rating systems is that very few people like the "Like" button. Thumbs up or down don't really express the nuance that civil, deliberative civic dialogue requires.  Now, we want people to behave in ways that are persuasive, informative and inspiring, so we figured the best way to do that is to subtly encourage people to judge one another with those criteria in mind. When you're contributing to a conversation at the Commons, it's hard to do that without feeling like you should try to be either persuasive, inspiring or informative. We feel like those ratings do a ton to help make conversation productive. And I'll tell you where we stole the idea: At TED.com, you can sort content according to the tags that people ascribe to talks--jaw-dropping, inspiring, etc. It was that sort of feeling we were going for.