Beyond algorithm updates, Google has made at least two major changes to its search engine this year: Search Plus Your World and the Knowledge Graph. The former was designed to offer users a search experience more tailored to their own personal web experience and social connections. The latter was designed to give users the info they're looking for without having to click off the results page to another site (while helping Google understand the meaning of the search in cases where there are more than one meaning).
When Search Plus Your World launched, it came with boxes on the right-hand side of some results pages. These were called "People and Pages" boxes. As Matt McGee at Search Engine Land points out, the new Knowledge Graph boxes (which CEO Larry Page calls "Knowledge Panels") have replaced the "People and Pages" boxes.
Before, for example, when you searched for a term like "music," Google would show the "People and Pages" box, highlighting specific musicians' profiles on Google+. Now, they'll show specific musicians, but rather encourage you to click, bringing up another search results page for that musician (complete with that musician's own personal knowledge panel).
If you click on Chris Brown from there, you get something like:
So, that's one way Google has toned down the Google+ in its search results. Of course, with this strategy, Google can point you to a page with an AdWords ad for an "ad related to Chris Brown". Google+ still doesn't have ads, so financially, this should work better for Google.
In March, Google made an algorithmic change, which seemed to favor Google+ profiles less as well. That changed was billed as:
Better indexing of profile pages. [launch codename "Prof-2"] This change improves the comprehensiveness of public profile pages in our index from more than two-hundred social sites.
When Search Plus Your World first launched, Twitter complained about Google favoring Google+ pages over more relevant Twitter pages. The aforementioned change seemed to have remedied that. Google+ profiles seemed to be ranking over more relevant profiles in less cases.
Another famous example was when Google was ranking Mark Zuckerberg's Google+ profile over his Facebook profile. That was also no longer the case. However, the Knowledge Graph has thrust Zuck's content free Google+ profile back into the spotlight: