Adult Internet users on social networking sites has quadrupled since 2005

It ain't just for the kids anymore.

The share of adult internet users who have a profile on a social networking site has more than quadrupled in the past four years -- from 8% in 2005 to 35% now, according to the Pew Internet & American Life Project's December 2008 tracking survey.

Here's the latest stats:

* 75% of online adults 18-24 have a profile on a social network site
* 57% of online adults 25-34 have a profile on a social network
* 30% of online adults 35-44 have one
* 19% of online 45 to 54 year olds have a profile
* 10% of online 55 to 64 year olds have a profile
* 7% of online adults 65 and older have a profile

I'm not surprised at these numbers given how many high school friends have come out of the woodwork friending me on Facebook recently : )