In the near future more and more users will access Internet services by means of portable devices through wireless links. However, mobile computing is still strongly limited by the scarcity of energetic resources of portable devices. In This work we propose and evaluate an application-independent energy management policy for a Wi-Fi hotspot scenario. Unlike the IEEE 802.11 power saving mode, the proposed solution is able to adapt to the application traffic profile, thus saving a considerable amount of energy. For the same reason it is flexible, i.e., it exhibits good performance irrespectively of the specific network application, and even in the presence of concurrent applications. Experimental measurements performed on a prototype implementation with different traffic types have shown that our energy management policy is able to save up to 80% of the energy consumed in a legacy architecture, without a significant degradation on the QoS perceived by the user.