It's fine to show off what you play around with in your spare time, but the very best and most productive workers actually won't have an extensive up-to-date Github repo. This is because they're been gainfully employed and have spent the vast majority of their coding time kicking ass at their real job.
Coming from the Rails world, this isn't true. Through my job, I fix problems with Rails or plugins I encounter. This may only account for say two percent of my development time, but that is significant enough to have a trail of pull requests.