Users really care about speed in interaction design...A snappy user experience beats a glamorous one, for the simple reason that people engage more with a site when they can move freely and focus on the content instead of on their endless wait.
0.1 seconds gives the feeling of instantaneous response. This level of responsiveness is essential to support the feeling of direct manipulation.
1 second keeps the user's flow of thought seamless.
10 seconds keeps the user's attention. A 10-second delay will often make users leave a site immediately.
In Broussa in Asia Minor, at the Green Mosque, you enter by a little doorway of normal human height; a quite small vestibule produces in you the necessary change of scale so that you may appreciate, as against the dimensions of the street and the spot you come from, the dimensions with which is is intended to impress you. Then you can feel the noble size of the mosque and your eyes can take its measure. You are in a great white marble space filled with light. Beyond you can see a second similar space of the same dimensions, but in half-light and raised on several steps (repetition in a minor key); on each side still a smaller space in subdued light; turning round, you have two very small spaces in shade.
From full light to shade, a rhythm. Tiny doors and enormous bays. You are captured, you have lost the sense of the common scale. You are enthralled by a sensorial rhythm (light and volume) and by an able use of scale and measure, into a world of its own which tells you what it set out to tell you.