The feature has been there for a few months. However, I only became aware of it a day or two ago.
Not only does Google surface results for Google+ (public posts and posts shared with you), but it also links to Twitter and Facebook!
Here is an example of what happens with the hashtag #socialmedia (I’m logged into my G+, Twitter, and Facebook accounts). Click the picture to see the zoomed version.
Not logged into your profiles? No problem! You can still see results for Google+ and Twitter.
Now, go have fun on Google Search! :-)