Google revealed a list of 39 changes it made in May, and one of them is about improving social search - particularly when Google chooses to show Google+ pages in the right-hand panel, often reserved for Knowledge Graph results.
Google's listing for the change says:
Updates to +Pages in right-hand panel. [project codename “Social Search”] We improved our signals for identifying relevant +Pages to show in the right-hand panel.
Pretty vague. It does show, however, that Google is still trying to figure out the best way to use its social network in search. Before the Knowledge Graph, there was a much greater emphasis on Google+ in this area of search results pages, but Google is really high on the Knowledge Graph results, and considers it to be one of the most significant things it has done for search in recent memory. Google also says Knowledge Graph has increased user searches.
When Google revealed Search Plus Your World earlier this year, it put a lot more Google+ content into users' search results, by default (although a good amount of this could be eliminated with the toggle button Google provides on the search results pages). Since then, Google seems to have toned the Google+ down a bit.
At SMX Advanced this week, Google's Matts reportedly acknowledged that the +1 is "not necessarily the best quality signal right now."
"It’s still early days on how valuable the Google+ data will be," he's quoted as saying.
That's not to say there isn't a great deal of value for webmasters to be using Google+. In another session at the event, Google+ was found to be a strong signal. A new study from Searchmetrics suggests that the quantity of +1's has the stongest correlation with good Google rankings (compared to Facebook shares and Tweets), but Google+ doesn't have enough users for them to be as significant.