A couple of screencasts have been created which cover the awesome new mobile (and responsive!) site which is included in GateIn 3.6.
The first one covers a brief overview of the mobile site that shows some of its cool new features and how it acts on a mobile phone.
The second screencast covers some of the configuration details when dealing with a mobile or responsive site. Including how to configure the viewport for the portal, restrict the shared layout to non-administrators and how to setup the responsive header portlet.
It also covers how to create a new mobile or responsive portal.