1) Social media engagement is now directly impacting search engine rankings through "social signals" like the number of times a site is mentioned or linked to on social media.
2) Google has introduced "social extensions" in AdWords like seller ratings and Google+ +1 buttons that allow social engagement directly on search engine results pages.
3) These extensions have not yet directly impacted Google's quality score metric but they are influencing key performance indicators like click-through rate and may influence quality score over time as Google considers more social factors in its algorithms. Marketers are experimenting with using these extensions to improve search advertising performance.