it's the little things
A fine example of this concept is illustrated in the differences between version 2 and the beta of version 3 of Apple's web browser, Safari. To make sense of the following screenshots, you also need to know that the keyboard shortcut to enter URLs is Command-L, and use a QWERTY-style keyboard.
The old version of Safari's shortcut to block pop-up windows was right next to the key sequence to move focus to the address bar. This would occasionally lead to inadvertent toggles of the pop-up blocker, leading to the occasional pop-up storm. Now the Safari shortcut adds in an extra shift key, reducing the likelihood that anyone would accidentally toggle the pop-up blocker status. It's not a major change, but it's one that pays off huge dividends in the user experience. Bravo, Apple.