In this study we analyse the structure of a particular form of collective decision-making in Wikipedia, i.e. decisions regarding content inclusion and deletion. Wikipedia’s official guidelines require that only topics that meet “notability” standards be included with a dedicated article. Decisions as to whether a topic is “notable” are made by groups of self-appointed reviewers, who assess the alleged encyclopaedic nature of a topic via so called “Article for Deletion” discussions. We analyse the structure and dynamics of these discussions in order to identify possible biases affecting their outcome. We show in particular the effects of voter heterogeneity and herding behaviour on the functioning of these collective deliberation processes.