This is a great resource for thinking about audience, and what people are currently doing online. The link below is to reports in the "Online Activities&Pursuits" category, but there are other relevant categories as well: Demographics, Internet Evolution, and Technology & Media Use to name a few. In addition to the reports, the site provides access to the datasets themselves, and charts and spreadsheets of their latest trend findings.

From their mission statement: "The Pew Internet & American Life Project produces reports that explore the impact of the Internet on families, communities, work and home, daily life, education, health care, and civic and political life. The Project aims to be an authoritative source on the evolution of the Internet through collection of data and analysis of real-world developments as they affect the virtual world."