User Interface Friction

In a short note posted on ACM Ubiquity, Andreas Pfeiffer describes the notion of "User Interface Friction":

We use it to describe and quantify the differences in fluidity and reactivity that exist between different operating systems, between software applications, even between different digital devices (music players, cameras, cell-phones, among others).

We can find examples of User Interface Friction in many places. Did you ever notice how menu behavior can slow you down when you are trying to access a command, like selecting a program from the Start menu in Windows? That's User Interface Friction. Did you ever remark how scrolling through long lists of songs on a MP3 player can be annoying? User Interface Friction again. In fact, any user interface has some degree of friction. Some of it we may not notice, despite that fact that it exists, other examples can be severely annoying. (...) User Interface Friction is inherent in any modern, menu-driven computer system and any device that sports a graphical user interface, and depends on a number of aspects, ranging from the speed at which the system displays a menu or sub-menu, to the efficiency of the mouse.