One of the metaphors I’ve always used when working on something—an application, a website, an article—is noise.
When something isn’t right, it makes a noise.
For instance, when I designed this site I worked on it until it was silent. (Your taste may vary, of course.)
Another example: this morning I’ve been dealing with menu item and toolbar item validation in an application I’m working on. When a menu item is enabled but it should be disabled it makes a crackly buzzing sound like a bug killer light.
It’s my belief that these things make a huge difference in user experience—the little things have to be right, or the app is noisy.