I love this graphic guide to social media sites like Twitter, Facebook, Reddit, Tumblr, etc. Mark Ragan linked to it on Twitter. It discusses and compares how good each site is for establishing or promoting a brand, talking to customers, driving traffic to a site, etc. Best quote: "Attempting to build your brand on Reddit is like trying to sell whale meat to Greenpeace. It won't happen, and it's likely to turn very ugly if you try."
You can read the guide here. Good stuff for anyone interesting in marketing or effective self-promotion.
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