Declaration: I'm a complete newbie to the GXT/GWT world. My expertise is in a completely different area of IT so please be gentle.
For the last 18 months I have been architecting a set of applications written in Java. Now it is time to look at the UI and hence that is why I'm looking at GXT - pure Java. Originally I liked to Portal concept but as soon as I saw the Desktop example I knew that it would the best solution.
I'm almost certain the demo comes in WAR form so you can just drop it into your servlet container and it should just magically work. Trying to build it and get it running yourself might prove to be a little frustrating.
The entire source code for the examples app and the desktop app are present in the GXT download zip, in the examples-src/ directory. There is no project setup in there though, only the Java files, the .gwt.xml files, and the image/css/html files needed to build the app, leaving you to setup the project in whatever IDE you wish.