1. A method, implemented by computing functionality, for providing usage information, comprising: receiving actual usage data from user devices operated by respective users, the user devices including a particular user device operated by a particular user, the actual usage data describing actual consumption of data by a set of applications that are run by the user devices, an application consuming data when it causes the data to be communicated via wireless communication infrastructure; generating application-level usage information based on the actual usage data, said generating comprising at least: generating personal usage information which describes actual consumption of data by a particular application run by the particular user device; and generating expected usage information associated with a candidate application provided by a marketplace system, the expected usage information describing an expected consumption of data by the candidate application upon running of the candidate application by the particular user device; receiving a triggering event from the particular user device operated by the particular user; and in response to the triggering event, providing either the personal usage information or the expected usage information to the particular user, depending on a type of the triggering event that has been received.