Excerpt from an overview of new Google+ Hangout features
Upgrade any conversation from long-form to live
Certain posts act as kindling for face-to-face interaction. Suppose your sister gets engaged, or your roommate lands a job, or your favorite singer shares their concert schedule. You can obviously write comments back and forth, but it's moments like these when you really want to connect in person. That's why we're making it easy to start a hangout from any post on Google+.
Just click "Hangout" underneath a post that you’re passionate about, and we’ll add your invitation to the comments. If others are hanging out already, you'll see their invitation in the comments as well.
Starting a hangout on a post (left); Joining a hangout already in progress (right)