Recently Gmail introduced a new feature that third-party add-ons had been doing for a while now which enabled you to get more info on the people that sent you any given email and also their latest updates from various social networks.
Now Google+ has been added to the list a natural and obvious move. But it's a move you're going to see repeated in countless other places and Google products.
Google's Mark Striebeck announced "A first tiny step: view recent Google+ posts in the Gmail people widget!" .
He said "You can now see the most recent Google+ post that the sender of the email shared with you in the Gmail people widget" . He also provided some insight into the whole process.
He explained "BTW: +Bella Kazwell is a tech lead on the Gmail team and +Steven Bills is the engineer who implemented this particular feature. Oh and before you ask unicorn is what we nicknamed our internal Gmail test environment" .
Google+ is just another data source for Google and it's hardly the most important at this point. But it's a data source that it controls entirely which is precisely why it wanted to have a social network of its own.
What's more it's why it didn't feel the need to strike a deal with Twitter to access the tweet firehose for its real-time search feature which got shut down until it can launch again with data mainly from Google+.