As far as I can tell, the sample is working on the server you linked. As Ian mentioned, the sample you are running looks a little outdated, the JavaScript Quickstart is the latest and greatest and uses the Google+ Sign-In button which has a number of enhancements, particularly when you are using client-side authorization.
To test that your sample is working, you can open the Chrome developer tools and run some simple client library code such as:
gapi.client.plus.activities.list(
{userId: 'me'}).execute(
function(resp){
console.log(resp);
});
If you see your activity feed, everything is working.
Regarding locally ... In order for the JavaScript library to work, you also must be running a web server on your computer such as the Python Simple HTTP Server:
python -m SimpleHTTPServer 8000
or Apache, twistd, etc.
If you directly open the file, permissions will prevent the library from working.
Your authorized JavaScript origins must also match the port (and protocol, e.g. https/http) that are set up in your Google APIs console project. If it's working remotely but not locally, you might be missing a localhost origin.