Until github goes down, and then they run `git remote add friend ssh://coworkers-workstation//path/to/repo` and push code to each other until github comes back up.
Well, pushing to someone else's local copy is a little harsh, since that copy probably won't be bare. Also git will slap your wrists if you try to do that. Instead, the coworker should pull from you. This is why GitHub's calls them pull requests.