Human Factor: How Long is Too Long to Users?

Traditional human-factor guidelines indicate that 0.1 second is about the limit for users to feel that the system is reacting instantaneously. One second is about the limit for a user's flow of thought to stay uninterrupted. Ten seconds is the maximum response time before a user loses interest.

However, nowadays users are "trained" to endure longer waiting time by the extensive use of modern AJAX methods to fetch and reload parts of a page in a as-need basis without the need to refresh the entire page. It is important to bear in mind that we should design website to aim for shorter response time.