[jsegura]

If we speak about human interactions, I think that it should be less than 250ms.

In 1968 Robert Miller published his classic paper Response time in man-computer conversational transactions in which he described three different orders of magnitude of computer mainframe responsiveness:

- A response time of 100ms is perceived as instantaneous.

- Response times of 1 second or less are fast enough for users to feel they are interacting freely with the information.

- Response times greater than 10 seconds completely lose the user’s attention.

But I totally agree with you, it totally depends on what is the purpose of your system.

[sebleon]

Good point, I wish this was better understood by the engineers at Gmail