Two days ago, I met Prof. Michelis, who just published the second edition of this “Social Media Handbuch” (in German). Interesting book, with some good summaries on forward-looking issues such as “Commons-based peer production”, “Wisdom of the crowd” etc.
Link to Book promotion – in German: http://www.nomos-shop.de/Michelis-Schildhauer-Social-Media-Handbuch/productview.aspx?product=14264