I mapped the companies on a scatterplot using Many Eyes (please be patient as this page can take time to load).  There were a few outliers like Starbucks so I took the log of both the mentions and followers to make the map legible.

The dots on the horizontal axis represent brands that do not officially participate in the conversations on Twitter (they have no followers).  The ones on the right hand side of the graph (Apple, Microsoft and AIG for example) are mentioned frequently in conversations so they might want to consider taking a more active role.  

For the brands that do have followers there seems to be a correlation between followers and mentions.  That makes sense intuitively.  Brands in the top right quadrant are very active and the ones on the bottom left are not.

If you draw an imaginary trend line through the scattercloud you would find brands on that line to have a number of followers that is in proportion to the volume of mentions they get.  Brands above the line however get followed more than they are talked about.  It’s the other way around for brands below the line.  If you mouse over the dots on the graph you see which brands fall where.

I think we need more data to really interpret the graph.  Being followed more than being talked about could be good or bad depending on the engagement levels of the followers.  Being talked about more than being followed could be good or bad depending on the sentiment of the conversations about the brand.  Even if the interpretation of this graph isn’t 100% clear, I thought I’d post it anyway as I think it is interesting to compare brands visually.  Would love to hear your thoughts.