Back when the Macintosh was first being designed, user testing suggested that many people had a hard time remembering what more than one button on a mouse was used for. So, they put one button on the Mac mouse.
They really seemed to feel the need for more functionality, though, so they added double-clicks as a short-cut to some extended actions. Of course, double-clicks were hard for some people.
So the cardinal rules of double-clicks were:
- Double-clicks should never be the only way to do something; they should simply be short-cuts
- A double-click action should be a natural extension of the single-click action
Of course, one of the big problems was that users ended up learning to always double-click. I’ve run into people who were genuinely surprised to learn that a single-click did anything. Even more people didn’t realize that there were other ways to accomplish double-click actions.
It’ll be interesting to see how Apple’s choice to have some functions on the new iPod shuffle only accessible through double- and triple-clicks and holding works out.