Within the last two days I wrote a new plugin, which allows you to jump faster between files of GWT services.
Using IDEAs “Related symbols” action you can jump from the async method in the interface to its implementation and vice-versa – all based on filename conventions and it is nice example of a GotoRelatedProvider.
Here you jump between files:
Here you jump between methods of files:
This plugin requires the community edition of IntelliJ IDEA.