Techniques are described for facilitating performance of tasks supplied by task requesters, such as by a task exchange server interacting with mobile task performer users available to perform tasks at various geographical locations. Some or all of the tasks may each be associated with geographical locations and/or other device-related criteria related to the performance of the task, and one or more mobile task performer users may be identified as being appropriate to perform the task based on the location of, qualifications of, and/or characteristics of mobile device(s) of the user. Such identified task performer users may then be notified of such appropriate tasks in various ways, such as by sending one or more electronic messages with information about the tasks to one or more mobile devices of the users, and may in some situations use one or more of their mobile devices as part of the task performance.