New research from the American Journal of Epidemiology:
Using this rich source of data, we were able to investigate the associations of Facebook use and of real-world social network activity with self-reported physical health, self-reported mental health, self-reported life satisfaction, and BMI. Although there were some variations in the significance of the different measures across outcomes, a clear pattern emerged. Our results showed that although real-world social networks were positively associated with overall well-being, the use of Facebook was negatively associated with overall well-being.
I'll be spending next weekend pouring over this data.