The Google Web Toolkit and The Google Eclipse Plugin both use the /war folder as base directory for the hosted mode web application. Maven users used to follow the maven-war-plugin convention for src/main/webapp.
You can change the maven-war-plugin configuration to use /war as web application source folder. The benefict of this setup is that you can define an alternate web.xml deployment descriptor, and have the hosted mode run a lightweight, test-only server. The war plugin webXml parameter can then be used to setup the real deployment descriptor to be used by your web application.
To use this setup you'll need to configure the gwt-maven-plugin in inline mode. The main side effect is that the /war folder will then contain classes and libs you have to exclude from your SCM (using svn:ignore).
To be even more productive you should also configure the build.outputDirectory to ouput classes into /war/WEB-INF/classes so that any change to a java source in your favourite IDE is immediatelly usable in the hosted browser with a simple refresh.
This is the recommended solution as you will then get a simple, productive environment with simple testing support
Another option is to configure the maven-war-plugin to build the exploded web application in /war, using the webappDirectory parameter. With this setup you won't see changes in your source folders but :