Research firm Radicati announced today that they expect the number of social networking users to rise from 798 million users in 2011, to over 1.2 billion in 2015. Since users typically have more than 1 account, they expect social networking accounts, including
both consumer and enterprise accounts, to grow from about 2.4 billion in 2011, to about 3.9 billion in 2015.

Given that the world’s population in 2015 is projected to be 7.2 billion, about one in six men, women, and children on earth will be socially networked. Another way to look at these numbers: Assuming the number of people connected to the Internet in 2015 will be about 4 billion (it’s about 2 billion today), we get a social networking penetration of only 30%.

Update: It’s Twitter’s 5th anniversary today.