Intellij's GWT support is great! I love the ease with which UiBinder classes can be made and the autocomplete/inspections support.
One thing that would save a lot more time would be the ability to create GWT custom events from the New -> GWT context menu. Each custom event requires a handler interface and an event model and creating each is quite repetitive. Here is an example of custom events:
It is my understanding that the GWT functionality isn't in the open source release of Intellij 9, so this isn't something I could add myself.