This paper studies information retrieval tasks related to web comments. Prerequisite of such a study and a main contribution of the paper is a unifying survey of the research field. We identify the most important retrieval tasks related to comments, namely filtering, ranking, and summarization. Within these tasks, we distinguish two paradigms according to which comments are utilized and which we designate as comment-targeting and comment-exploiting. Within the first paradigm, the comments themselves form the retrieval targets. Within the second paradigm, the commented items form the retrieval targets (i.e. comments are used as an additional information source to improve the retrieval performance for the commented items). We report on four case studies to demonstrate the exploration of the commentsphere under information retrieval aspects: comment filtering, comment ranking, comment summarization and cross-media retrieval. The first three studies deal primarily with comment-targeting retrieval, while the last one deals with comment-exploiting retrieval. Throughout the paper, connections to information retrieval research are pointed out.