Visible Technologies posted a list of some of the best Social Media industry reports of 2008.  All but one of them are free.  The first, from my former Razorfish colleagues, is quite comprehensive and insightful.

• Razorfish: FEED: Consumer Experience Report: This study focuses on understanding how technology impacts today’s digital consumer experience.
• Technorati: State of the Blogosphere 2008: The long time industry standard, this year’s report analyzed trends and themes of blogging and surveyed bloggers about how blogging has impacted them personally, professionally, and financially.
• Universal McCann: Power to the People Wave Report 3: This excellent study measured consumer usage, attitudes and interests in adopting social media platforms and technologies.
• Forrester Research: How to Connect with Bloggers: This paid report helps brands understand bloggers and their motivations before kicking off outreach programs.
• MarketTools Insight: How Americans are Socially Connected on the Web. This report covered the link between socially networked consumers and purchasing decisions.

Also from Razorfish:

Due to popular request, today we are releasing Meet The Connected Consumer, a PDF download that contains our Digital Consumer Behavior Study *and* all of the data. This includes the majority of questions we asked respondents and a detailed quantitative breakdown of their responses.

The FEED Consumer Experience Report includes much of the Meet The Connected Consumer content.  But the Connected Consumer report includes the supporting data.