The proliferation of ontologies in the public domain and the ease of accessing them offers new opportunities for knowledge sharing and interoperability in an open, distributed environment, but it also poses interesting challenges for knowledge and Web engineers alike. In this paper we discuss and analyse those challenges with emphasis on the need to evaluate publicly available ontologies prior to use. We elaborate on a number of issues ranging from technological concerns to strategic and political issues. We drawn our experiences from the field of ontology mapping on the Semantic Web, a necessity that enables many of Semantic Web's proclaimed features
