Brian forwarded some info from Wikipedia on the Pareto principle - we were talking about UX issues. 80/20 is NOT about picking low-hanging fruit:
The 80/20 rule is often used but frequently misunderstood. The 80/20 rule means that, in most situations, 80% of the effect is a result of 20% of the effort. For example, 80% of a company’s revenue probably comes from 20% of its customers. When applied to UX design, this rule implies that concentrating on improving the most important 20% of the system will result in an 80% improvement in the overall experience. The task for the feature team, then, is to determine which 20% to improve that will cause 80% of the improvement in the overall experience.
To put it another way, displaying and improving the right 20% of the properties on a property sheet will improve the experience 80% of the time. The rest of the features can then be accessed through an Advanced command button. The challenge is to identify which 20% of the properties to display and improve.