I came across a really interesting blog post by Jensen Harris, on Fitt’s law and new Microsoft Office “Ribbon” user interface.
Fitts’ law is a model of human movement, predicting the time required to rapidly move from a starting position to a final target area, as a function of the distance to the target and the size of the target. Fitts’ law is used to model the act of pointing, both in the real world, for example, with a hand or finger and on computers, for example, with a mouse. It was published by Paul Fitts in 1954.
Reference: Wikipedia on Fitt’s Law