Ok, so I’m not saying that we need to know the maths, but the underlying principles are important! Fitts’ Law tells us that the time to acquire a target is a function of the distance to and size of the target, so the size of a link area and it’s position on the page (and relative to other elements) is important. Hick’s Law says that the time it takes for a person to make a decision is a result of the possible choices he or she has. More choices mean a longer decision process – which gives us the 7 plus/minus 2 rule.
These are two of the fundamental rules that I use in user experience architecture. I’d recommend Tog’s (Bruce Tognazzini’s) First Principles of Interaction Design for some more.