You grant some rights to other users of GitHub, but I'm not seeing anything that prevents proprietary code:
> If you set your pages and repositories to be viewed publicly, you grant each User of GitHub a nonexclusive, worldwide license to access your Content through the GitHub Service, and to use, display and perform your Content, and to reproduce your Content solely on GitHub as permitted through GitHub's functionality. You may grant further rights if you adopt a license.
Soon as I see that, I've got to close the tab, so does anyone who cares about IP.
(disclaimer: i'm a co-founder of ScaleFT)