The whole site is built using Google Webtoolkit (GWT) and hosted on Google AppEngine - pages for now are coming from a JSON file. This will change once we finish building the cms backend using the datastore - more on that later.
Before starting the project we did investigate number of other AppEngine Java based CMS projects - many are frankly bloated. We felt the clear need to keep things simple.
One issue which we are aware of is that the site at this stage has the worst SEO (look at the source) - we intend to fix that by having a html page generated on fly, only when requested.