GitHub now enforces the User Agent. If you do API calls without user agent you will get a 403 error message back. Check out this post: http://developer.github.com/changes/2013-04-24-user-agent-required/.
If you are using the HTTParty GEM in Ruby to do the API calls you have to set the headers. Here an example:
body = HTTParty.get(url, :headers => {"User-Agent" => "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_8_2) AppleWebKit/537.17 (KHTML, like Gecko) Chrome/24.0.1309.0 Safari/537.17" } ).response.body
Robert Reiz 