Research on energy-efficiency of communication networks has already gained the attention of a broad research community. Specifically, we consider efforts towards improving environmental sustainability by making networks energyaware. An important step in this direction is establishing a comprehensive methodology for measuring and reporting the energy consumption of the network. In this work, we compare and contrast various energy-related metrics used in the recent literature, by means of a taxonomy definition, as well as through relevant case studies. We believe this to be a first necessary step towards the definition of a common framework for the performance evaluation of energy-aware networks.