Graphs like these are a great tool when explaining the importance of social media marketing to management and groups of professionals unfamiliar with the benefits of social media. In the past, the merits of sites like Flickr and reddit have been debatable in the corporate world, but this updated chart does a great job of explaining the levels of importance for each channel. It also now includes tumblr (which, in my opinion, means posterous is included as well), allowing for easier explanation as to how/why these sites have become mainstream tools for many brands and organizations. Thanks CMO.com for updating the graph!
For a full-size pdf: Social Media Landscape 2011
Single Girl in a Working World 