New file button = New Post (rich editor)
Branch and new file = Draft
Edit button (owner) = Edit
Edit button (reader) = Submit correction
Pull request = Submit Guest post
Pull request comment = Copy/content editor
Issues = Idea/Suggestion bucket
Commit button = Publish and deploy
If there was a way to do the live markdown preview using the css (maybe you could inline link it?), then you have a pretty complete blog engine for hackers. This would be an awesome feature IMO.Github would then be the place where you put your code, write your blog, track your issues, paste snippets for IRC (Gist), display your business card (profile info), and host your talk slides (SpeakerDeck). The next logical step to me would be integrating conferences/user groups (ala Lanyard/Meetup.com).
PS. @github feel free to hire me to help build it out :P