Another factor is what the user perceives as reasonable delay. As stated in Chapter 1, Faster Web—Getting Started, this is directly related to what the user considers to be the optimal performance of a certain type of application. This optimal performance is often determined according to what the user might consider to be an application of reference. In the case of web-based applications and websites, there are certain thresholds to be taken into account as they are shared amongst all web users on average.

Firstly, most users consider a response time of 300 milliseconds or less to be instantaneous. This is in great part explained by the previously mentioned "consciousness lag." As for response times between 300 milliseconds and 1 second, these are considered to be a reasonable delay and give the user the impression of a smooth transition. Many users will start losing attention and begin feeling impatient beyond a three second delay in response time unless...