Git notifications
When you go to main github page and log in you will see a news feed where you can read about changes to repositories and wikis that you are watching.
Also you can subscribe to the rss feed:
https://github.com/blog/1214-notification-email-improvements
Link about wiki notification options
This link may be interesting:
http://alexking.org/blog/2011/11/28/not-getting-github-notifications