An ever-growing number of users participate in online communities such as Flickr, del.icio.us , and YouTube , making friends and sharing content. Users come to these sites to find out about general trends – the most popular tags, or the most recently tagged item – as well as for more specific information, such as the recent posts of one of their friends. While these activities correspond to different user needs, they all can be seen as the filtering of resources in communities by various search criteria. We provide a survey of these search tasks and discuss the challenges in their efficient and effective evaluation.