I'm a CS associate professor. I teach a course which consists in contributing to a free software, in third year at my uni. A few years ago a couple of students decided to make a contribution to GNU ls. The change was to have the output color independent of capitalisation (it is based on filename extension). Their code was accepted. It was a tiny tiny contribution, but it's probable that these few lines of code are and will be executed a few thousands times more than all other contributions my other students made.