We extend the notion of social tagging to construct social summaries of complex multimedia materials. Our system allows students to apply time-indexed multimedia tags such as handwritten annotations or photos to different parts of lecture recordings. These tags can be used to straightforwardly access different parts of the lecture. The social component of the interface presents information about which tags are most frequently accessed by others: allowing students to infer those parts of the lecture of most interest to others. We demonstrate the utility of the approach in a 6 week fieldwork study. Social summaries are used much more than corresponding systems that do not provide social information. In addition, social tool use was correlated with high course marks. Author Keywords Tagging, Collaborative Systems, Notes, Photos, Popularity, Speech Browsing, Speech Retrieval, Web2.0. ACM Classification Keywords H5.m. Information interfaces and presentation (e.g., HCI): Miscellaneous.