@christian: you said that 'retailers certainly have to adapt new forms of communication' can we classify this form (social media) like e-commerce system?
Social networks can be given full functional online stores. To this end, social communities are special applications that help users to make the entire buying cycle does not go out of network. In addition, social networks have a number of advantages, which are as user activity: comments, views, opinions, recommendations, discussions, and more.
Importantly, one of the most important, the marketing advantages of social networking - is the users themselves. Sharing information, users can make a very powerful viral advertising. But unfortunately, or fortunately, often such "viral advertising" ruining unscrupulous entrepreneurs.
Just from experience I can say that the criticism of the online store customers affects its politics. Customers help shape the assortment. Their reviews, they help to fall into the trend of the season.
However, very strong players yet social networks should not be used for the main site.
Sorry for the little English. Thank you for your interest.