A Google researcher saw a 1/2 second page delay cause a 20% drop in traffic and revenue.
On this post, an Amazon.com employee concurred; In A/B tests, we tried delaying the page in increments of 100 milliseconds and found that even very small delays would result in substantial and costly drops in revenue.
Based on the above quote let's simplify and say revenue drops off linearly with the delay of the appearance of page, with a delta based on the Google research. Taking into account Amazon.com's Revenue for 2007 was USD $14.835 Billion…
500ms = 20% loss = USD$ 2.967 Billion loss
100ms = 4% loss = USD$ 593,400,000
1ms = 0.04% loss = USD$ 5,934,000
By this logic, every extra millisecond the page takes to load costs Amazon.com almost six million lost dollars in revenue.
(btw, I know UI&us is currently loading slowly and realize the hypocrisy! I'm working on this problem with someone already. Any tips are welcome.)