Speed matters to users
Long ago, I heard that IBM did a study on usability and found that people's minds will start to wander after 100 milliseconds. Is it true? I asked a search engine, but the Internet hung and I forgot to try again.
Anyone who ever used IBM's old green-screen apps hooked up to an IBM mainframe knows that IBM built its machines as if this 100-millisecond mind-wandering threshold was a fact hard-wired in our brains. They fretted over the I/O circuitry. When they sold the mainframes, they issued spec sheets that counted how many I/O channels were in the box, in the same way car manufacturers count cylinders in the engines. Sure, the machines crashed, exactly like modern ones, but when they ran smoothly, the data flew out of these channels directly to the users.
The real Web is never as fast as the office network
This is an easy mistake for programmers who are in love with browser-based tools that employ AJAX everywhere. It all looks great in the demo at the office. After all, the server is usually on the desk back in the cubicle. Sometimes the "server" is running on localhost. Of course, the files arrive with the snap of a finger and everything looks great, even when the boss tests it from the corner office.
But the users on a DSL line or at the end of a cellular connection routed through an overloaded tower? They're still waiting for the libraries to arrive. When it doesn't arrive in a few milliseconds, they're off to some article on TMZ.
Algorithmic complexity matters
On one project, I ran into trouble with an issue exactly like Richard in "Silicon Valley" and I turned to someone below the drinking age who knew Greasemonkey backward and forward. He rewrote our code and sent it back. After reading through the changes, I realized he had made it look more elegant but the algorithmic complexity went from O(n) to O(n^2). He was sticking data in a list in order to match things. It looked pretty, but it would get very slow as n got large.
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