The presence of Google+ is definitely growing as it continues to become a significant part of how we interact with many of Google's services. Early this year, the social network branched out to become a sign-in solution for virtually any kind of app or website. With an announcement yesterday, Google+ is now set up to accept sign-ins from Google Apps users and accounts without an actual Google+ profile. If that weren't good enough, the permission system has been greatly improved to support "incremental auth," which allows apps and websites to request only vital permissions to begin using them, and then ask for new permissions once the user is logged in.
If you caught the announcement of Google Play Services 3.0, aka "Google+ Sign-In," you're already halfway up to speed on this. Google Play Services is an APK that many of Google's apps rely on to hook into Google+ and, just like the Play Store, Google has the ability to silently update it.