I love this story from the Steve Jobs bio:
One day Jobs came into the cubicle of Larry Kenyon, an engineer who was working on the Macintosh operating system, and complained that it was taking too long to boot up.
Kenyon started to explain, but Jobs cut him off. “If it could save a person’s life, would you find a way to shave ten seconds off the boot time?” he asked.Kenyon allowed that he probably could.
Jobs went to a whiteboard and showed that if there were five million people using the Mac, and it took ten seconds extra to turn it on every day, that added up to three hundred million or so hours per year that people would save, which was the equivalent of at least one hundred lifetimes saved per year. “Larry was suitably impressed, and a few weeks later he came back and it booted up twenty-eight seconds faster” Atkinson recalled.
For me this beautifully sums up why things like website performance and effortless user experience matter so much. You may not have 5 million users interacting with your website but even low levels of traffic soon mount up.