I recently read a great report put out by Forrester on social networking, who's doing it, why they are doing it, where it is headed, and all kinds of other data goodness.  Below is a very interesting chart from the report.  For a small business online marketing strategy, social networks can plan a very cost effective role. More good news?  The household income of social network users is quite appealing, making them a great target for online marketing efforts.  Bombs away.

Social network demographics