As I understand it, the UI folks at Nintendo who were working on the Wii controller did user testing, of course. In one test, they would hand a new user a controller wand with instructions to "Just draw stuff on the screen" using a simple drawing program.
The metric Nintendo came up with was called TTP, or the how long in minutes and seconds -- sometimes, only seconds -- before the user drew the inevitable male genitals. "Time To P-n-s". Averaged something like two or three minutes.
Every new vista humankind opens will be so decorated. And so, World of Text: QED. :-)