EDIT: And the karma DOES matter if you want to get new opportunities via stackoverflow careers. I have landed a job recently via SO and chatted with the recruiter a bit about their experience with the platform. He told me some companies specify they want to hire from the pool of Top X% in given technology. Another thing is the response rate on SO is dramatically better than Linkedin, which doesnt surprise me: I do my best to answer every SO Careers message while I mostly ignore Linkedin recruiters.