Mashable lists a series of recent sources for statistics on social media:
1) The Society for New Communications Research’s “New Media, New Influencers & Implications for Public Relations” (.pdf). They “set out to conduct an examination of how influence patterns are changing and how communications professionals are addressing those changes by adopting social media. ”
2) Universal McCann’s Social Media Research Wave 3 (.pdf) research report, whose goal is to “measure consumer usage, attitudes and interests in adopting social media platforms ”
3) The University of Massachusetts Dartmouth Center for Marketing Research recently released “Social Media in the Inc. 500: The First Longitudinal Study” (.pdf)
4) Comscore recently released statistics on worldwide usage of social networking sites
5) A Rapleaf study revealed gender and age data of social network users
What it means: for data-oriented people like myself, it’s always good to have a handy list of credible statistics resources.