Content on Google+ can be promoted within the search results of the people you are connected to by email.
It apparently works when you’re logged into Gmail. When searching for content that your friends/connections have engaged with on Google Plus, this content related content will appear at the top of the results generated.
Due to the small but growing Google+ population and the differences between your own connections you email and those you are connected with on Google+, this is a minority bonus for the super loyal Google fans. It’s an interesting to know feature that has been noticed, but due to the small audience numbers on Google+ this is only going to benefit very few people and brands.
Not something to make a campaign about, but it is a sign of how the integration of Gmail and Search Results are becoming more integrated. Something that is made more possible with the Schema mark-up.