Social Media Infrastructure
The social justice/activism side of social media has not been explored nearly enough. The basic work of sharing information is a form of activism in itself, and connecting people who would not otherwise know about each other or be connected is a way of leveling the playing field to some degree, bringing those without voice (ideally) together in some way with those who do. I think twitter has shown well that its real and potential uses in social activism are varied and extensive.
All social media APs can be used for social activism. The very nature of social media is to allow the masses to connect with one another without "big brother" controlling the means of communication. Social Media will be the most liberated form of mass communication in history if it isn't already. There's no going back from this point.