Awesome add-on. Used it for about a month now, and I'm starting to forget where GitHub ends and Refined GitHub begins.
I experienced a slight conflict between Refined GitHub and Vimium. Both add-ons provide their own keyboard shortcuts, which overlap in some cases. However, I found that the conflicting hotkeys could be disabled by toggling the related options in the Refined GitHub preferences.
A lot of hard work has gone into this project, and it shows. If you spend any significant time on GitHub, this add-on is a must.