UPDATES: Links added.
Due to security reasons, certain people who were shot on video asked for the Youtube clip shot at the International Development Week Workshop to be removed from the Internet. In order to show them how quick and easy it is to publish a video on their own website (or blog) I embedded a video of mine instead.
Good rule of thumb: Go where your audience is. If they are on myspace, go on myspace. You can be on Facebook, but focus your time and energy by updating and being involved on Myspace. Same for Youtube vs Seesmic vs Viddler.
Another rule of thumb: Don't be afraid to ask questions.
As promised, here is the list of social media sites discussed at the workshop: