The Nuances of Using Fitt's Law

Design "laws" and "principles" are incredibly helpful in creating a consistent and high quality product, but since all projects and people are different, you should only apply design principles with their nuances in mind.

The When You Shouldn't Use Fitts's Law To Measure User Experience article published in Smashing Magazine today does a great job illustrating some of the pitfalls of blindly following Fitt's Law.

The key statement of Fitts’s Law is that the time required to move a pointing device to a target is a function of the distance to the target and its size. In layman’s terms:the closer and larger a target, the faster it is to click on that target. This is easy to understand, not too difficult to implement and it doesn’t seem to make much sense to contradict such a simple and obvious statement.

However, before you start applying Fitts’s Law on every single pixel you can find, consider a few problems that might arise for you as an interaction designer.
— http://uxdesign.smashingmagazine.com/2012/12/04/fittss-law-and-user-experience/