My personal note. (CMIIW is one of my gods). This is written in 2011, hence it might or might not work with latest update (if any).
This is the very basic and simplest example to access Google+ activities via its API, using HTML, JQuery and simple API key authentication.
All client side scripts. There is no server side scripts is being involved.
The only weakness of the codes is: I need to hide my API key somewhere in the server's inaccessible folder.
But it can be overcame when I use the code in real application, by deploying the HTML file into a web server.
Since it's contained in a HTML file, it can be utilized in non-native mobile application, such as HTML5 app runnable in mobile devices. I also imagine blog (Blogger, Wordpress) sidebar-plugin and browser's add-ons.