Speed
Pages must react in 0.1 second for the to feel that the system is reacting instantaneously to his or her requests.
Pages that react in about 1.0 second will allow the user's flow of thought to stay uninterrupted, even though he or she will notice the delay. The user does lose the feeling of operating directly on the data.
Pages that react in more than 10 seconds will loose the user’s attention, especially without feedback. Feedback during the delay is especially important if the response time is likely to be highly variable, since users will then not know what to expect.