The concept of social networks is widely used to model mutual relationships between people (but also between other objects like chemical compounds). Intriguing problems from this area range from finding important structural patterns that influence interaction among the considered actors across sentiment analysis that studies people´s opinions, emotions, and attitudes to the analysis and evolution of the network structure itself. Recently, the trends have shifted rather towards online social networks (e.g., Facebook, LinkedIn and MySpace) which allow for efficient data collection.