It looks like there is great interest to quantifying performance impact on business, linking response time to income and customer satisfaction. A lot of information was published, for example, the Aberdeen Group report, “Customers Are Won or Lost in One Second”, or the Gomez whitepaper “Why Web Performance Matters: Is Your Site Driving Customers Away?” There is no doubt that there is a strong correlation between response times and business metrics and it is very good to have such documents to justify performance engineering efforts—and some simplification may be good from the practical point of view—but we should keep in mind that the relationship is not so simple and linear and there may be cases when it would matter.
Response times may be considered as usability requirements and are based on the basic principles of human-computer interaction. As long ago as 1968, Robert Miller’s paper “Response Time in Man-Computer Conversational Transactions” described three threshold levels of human attention. Jakob Nielsen believes that Miller’s guidelines are fundamental for human-computer interaction (http://www.useit.com/papers/responsetime.html), so they are still valid and not likely to change with whatever technology comes next. These three thresholds are:
Users view response time as instantaneous (0.1-0.2 second)
Users feel they are interacting freely with the information (1-5 seconds)
Users are focused on the dialog box (5-10 ...