By answering questions on stackoverflow, the person is essentially teaching neighbors, teenagers, and "friends" by creating an open "wikibook". Teaching is one

By answering questions on stackoverflow, the person is essentially teaching neighbors, teenagers, and "friends" by creating an open "wikibook". Teaching is one of the best ways to learn something. If you can successfully teach a concept, then it shows deep understanding. As long as HN or stackoverflow doesn't take up too much productivity, having a high reputation/karma could be a good thing. It shows passion.