I've started circling G+ friends in theme circles when they post things related to my own interests. Wait, what?
It's easy to GET posts in my stream based on my interests -- just follow people who talk about them. But I'd also like to SEND posts to people who share my narrow interests, without annoying the larger group.
So now I have circles that categorize topics, rather than people. I made circles called "Food," "Health," "Politics," and others.