We present in this chapter a review of current work that leverages on large online social networks' meta-information, in particular Flickr Groups. We briefly present this hugely successful feature in Flickr and discuss the various ways in which metadata stemming from users' interactions with and within groups has been exploited by researchers to improve on state-of-the-art search and browsing algorithms. We then review recent works that have already made use of Flickr Groups, either as a data source, as a way of filtering content, or as a way to reach users for automatic analysis or user studies, and conclude by pointing out to potential directions of future research.