Twenty percent of all input forms filled out by people contain bad data.
From an operating system research point of view, Unix is if not dead certainly old stuff, and it's clear that people should be looking beyond it.
A program designed for inputs from people is usually stressed beyond breaking point by computer-generated inputs.
At least for the people who send me mail about a new language that they're designing, the general advice is: do it to learn about how to write a compiler