System response time research is an important issue in human-computer interactions. Experience with technical devices and general rules of human-human interactions determine the user's expectation, and any delay in system response time may lead to immediate physiological, emotional, and behavioral consequences. We investigated such effects on a trial-by-trial basis during a human-computer interaction by measuring changes in skin conductance (SC), heart rate (HR), and the dynamics of button press responses. We found an increase in SC and a deceleration of HR for all three delayed system response times (0.5, 1, 2 s). Moreover, the data on button press dynamics was highly informative since subjects repeated a button press with more force in response to delayed system response times. Furthermore, the button press dynamics could distinguish between correct and incorrect decisions and may thus even be used to infer the uncertainty of a user's decision.