This is a load of BS. I know <i>great</i> developers who don't waste their time on sites like GitHub and StackOverflow (that's probably why they're great developers to begin with). I look at it like this - if a prospective company is so clueless they can't discern what a good developer is for their organization then do you want to work for them? How are they going to handle performance reviews? Look at your GitHub contributions?