In collaborative software development projects, work items are used as a mechanism to coordinate tasks and track shared development work. In this paper, we explore how “tagging,” a lightweight social computing mechanism, is used to communicate matters of concern in the management of development tasks. We present the results from two empirical studies over 36 and 12 months, respectively, on how tagging has been adopted and what role it plays in the development processes of several professional development projects with more than 1,000 developers in total. Our research shows that the tagging mechanism was eagerly adopted by the teams, and that it has become a significant part of many informal processes. Different kinds of tags are used by various stakeholders to categorize and organize work items. The tags are used to support finding of tasks, articulation work, and information exchange. Implicit and explicit mechanisms have evolved to manage the tag vocabulary. Our findings indicate that lightweight informal tool support, prevalent in the social computing domain, may play an important role in improving team-based software development practices.