Inspired by the fantastic idea of explaining a number of Social Networks using nothing but donuts which Douglas Wray posted on Instagram, I have expanded it with a couple more networks.
No doubts this will need frequent updating, and perhaps all those who are engaging in some form of education on Social Media could adopt it as the universal metaphor. I, for one, surely will.
Update: I have developed a more international version now, including RenRen (China) and Vkontakte (Russia); and before you ask, yes I learned how to pronounce these phrases and what they mean !
Update june 5, 2012: there is an updated version of this chart here.