When Weber Shandwick broke down social visibility more granularly, nearly every channel saw an increase in CEO participation. Facebook made the biggest leap among the social networks, with one out of 10 CEOs using the channel for visibility, up from 4% in 2010. However, Twitter was notably the only channel that saw a decrease in CEO participation. This is likely because engagement was high in 2010—double Facebook’s level—and enthusiasm may have waned as marketers discovered that the fast-moving mircroblog was too contentious and time-consuming a place for CEOs who first and foremost need to protect the brand image. Read the rest at eMarketer.