This is my second or third biggest problem with GitHub. If I want to submit a patch—the thing that Git was made for—I cannot use GitHub to do it. Assuming one has already gone through the "create a GitHub account" step, my closest option is to go to github.com to create a completely unnecessary on-GitHub "fork", go back to my local copy to add that remote and push to it, and then go back to the github.com and click around to submit a pull request.
Pull requests in Git were designed for trusted, frequent collaborators. I.e., project maintainers that are routinely syncing with one another. It's not supposed to be the preferred mechanism for ordinary contributions, and certainly not for drive-by contributions.
My biggest gripe, though, is that the on-GitHub fork from the first paragraph will live on in my namespace forever, unless I manually prune it. And even if I do prune it, I still have no way to control the fact that GitHub has silently set up a social networking timeline to broadcast a centralized index of all this activity to anyone and everyone, without asking me, and without a way to manage the stuff that goes into the timeline, control who it's shared with, or turn it off completely.