1. A method in a sharer computer system for providing enhanced application behavior in the presence of application sharing in which output of an application being shared is provided to viewer computer systems for display at the viewer computer systems, the method comprising: executing an instance of an application that is being shared, the executing instance of the application performing acts that include: receiving from an application sharing program an indication that the instance of the application is being shared and an identity of a user who is controlling the application, the application sharing program for sharing applications between the sharer computer system and the viewer computer systems; and adjusting the behavior of the instance of the application being shared according to the identity of the user that is controlling the instance of the application being shared wherein the adjusting includes changing output of the application, displaying the changed output at the sharer computer system, and displaying the changed output at the viewer computer systems wherein the adjusting of the behavior of the instance of the application according to the identity of the user who is controlling the application includes changing a user interface of the application to match a preference of the user who is controlling the application.