Recently, Masters in Marketing posted this fantastic infographic that gives a perfect overview of the current state of affairs in the social media space.
Some significant take-aways:
Over 60% increase in adult internet users using Facebook
40-80% increase in overall social media participation for users over 30
20% of all internet users over 18 are active on LinkedIn
Between Q2 and Q3 of 2013, there was a 15% increase in usage of LinkedIn