The User Experience (UX) is a crucial factor for designing and enhancing the user satisfaction when interacting with a computational tool or with a system. Thus, measuring the UX can be very effective when designing or updating a Web site. Currently, there are many Web sites that rely on collaborative tagging: such systems allow users to add labels (tags) for categorizing contents. In this chapter the authors present a set of techniques for detecting the user experience through Collaborative Tagging Systems and we present an example on how to apply the approach for a Web site evaluation. This chapter highlights the potential use of collaborative tagging systems for measuring users' satisfaction and discusses the future implications of this approach as compared to traditional evaluation tools, such as questionnaires, or interviews.