1. A contact evaluation system of a computing system comprising: a contact sensing unit that senses a first set of one or more contacts on or near a touch sensor surface at a first time and produces first information regarding the first set of sensed contacts, and that senses a second set of one or more contacts on or near the surface at a second time, after the first time, the second set including the first set, wherein the first set maintained contact with the sensor surface during the time period between the first and second times, and produces second information regarding the second set of sensed contacts; and an event generator that evaluates the first information to determine whether the first information satisfies a first predetermined criteria, initiates a first input event as a command to the computing system based on the resulting determination that the first information satisfies the first predetermined criteria, evaluates the second information to determine whether the second information satisfies a second predetermined criteria, the second set of one or more contacts remaining in contact with the sensor surface during the evaluation of the second information, and cancels the initiated first input event based on the resulting determination that the second information satisfies the second predetermined criteria, wherein cancelling the initiated first input event prior to the performance of the first input event includes deleting the first input event from the input event queue.