One of the interesting features of Google+ is the Explore button. Clicking it reveals "What's hot and recommended" on Google+ (it used to be called "Hot on Google"). These are the posts that are trending, and in fact, to the right of your stream you will see a list of the Google+ hashtags and conversations that are literally trending. You can check out this feed any time you want, and control how many of these items get into your Home stream. But have you ever thought about what it takes to get into "What's Hot?"
Understand that having a post get into the Explore stream should be every marketer and small business owner's dream. Instead of your post being limited in visibility to people who have circled you, a post that shows up in What's Hot can show up in countless other people's streams, giving you potential exposure to millions of Google+ users.