I host repositories on GitHub. I've noticed as of the 7 beta, the UI to authenticate is disabled. As a result I can't get any authentication settings into or out of XCS, so XCS can't access my repositories.
http://i.imgur.com/Ilpjgqx.png
I've looked briefly through the XCS logs trying to understand what's going on here and there's nothing obvious.
See also rdar://21334520