Enabling you to thank your friends for a helpful result
Google+ is just an evolution of Google, that's what the company always says; so, in that regard, even more integration with its other products, especially search, isn't much of a surprise.On the other hand, any little bit that can help drive engagement with Google+ helps, despite Google saying that the social network is doing great and despite naysayers claiming that all that Google really cares about is your identity not whether you actually use Google+ or not.
Which explains Google's latest Google+ trick, you can now thank people that have +1'ed something you found in your search results. The idea is to highlight the fact that +1'ing something has actual results, i.e. your friends will see your actions in search results.
But believing that is a matter of faith, with the new "thank you" link, which posts a Google+ thank you note, you get to see that your actions are really seen by your friends.