Particularly from the point of view of Operating Systems and Web Browsers...<p>For example:<p>Does 80% of the code come from 20% of the functionality?<p>Do 80% of bugs come from 20% of features?<p>Does 80% of software complexity come from 20% of the functionality?
I would say generally, "Yes."<p>Definitely 80% of the bugs will come from 20% of the features. 80% of the usability and attraction is also from 20% of the features, but not necessarily the same ones.<p>Perhaps relatedly, about 70% of all software work is diagnosis and debugging. So a small subset of (maybe not so important) features causes most of the overall work in the project.