Please consider this a draft until GWT 1.6 is officially released
Upgrading to GWT 1.6
There are four tasks involved when upgrading a GWT 1.5 project to a GWT 1.6 project:
Download the new JAR files and update your launch configurations.
GWTShell has been replaced by HostedMode, so you will need to update your Eclipse project settings accordingly.
GWT now uses a war directory for most public resource and server configuration files. The war directory is a standard directory recognized by many web servers, including GWT hosted mode.
Event listeners have been replaced by event handlers.