ReadWriteWeb published notable demographic info from research from Pew Internet and American Life showing Who's Online and What Are They Doing There.
Predictably, younger people are using more social networks while older people are using the internet to research and utility.
This report could be useful in determining your audience as you construct a social media strategy.
Also, Brian Solis looks at what platform is being used for the Top 100 blogs. Guess which platform is used the most.
There are many blogging platforms out there. This could help narrow it down when making a decision as to which on to use.