Following are some good posts with further evidence of the impact of webpage/webapp responsiveness to the user experience, amount of usage and ultimately revenue.
Good introductory quote to the external links and images shown below:
There’s no longer any debate. There’s reliable, reproducible evidence that web page latency is directly tied to the bottom line. At Velocity, Microsoft, Google and Shopzilla made this abundantly clear in a series of awesome presentations: detailed, controlled testing proves that slower pages hurt the bottom line. In Google’s case, adding delay reduces the average number of searches a visitor does each day even after the delay is removed.
Regarding “smaller scale” sites more typical than Google and Bing:
The results of their analysis show how significant a reduction in page latency can be. In addition to reducing bounce rates, and increasing pages per visit & time on site, they found a 16.07% increase in conversion rates and a 5.50% increase in average order value. – http://radar.oreilly.com/2009/10/watching-websites.html
Good summary PDF showing metrics of performance impact.