If you don't want to modify the widget appearances or behaviors, Ext-GWT is nice.

If you aren't building a large web-app, Ext-GWT is the way to go.

But if you're one of them people who prefer to do TDD, or unit-test etc, avoid Ext-GWT at all cost.

If you want to personalize your app, avoid Ext-GWT at all cost.

If you want a solid (library) Java code, avoid Ext-GWT at all cost.

I've been using their code since MyGWT 0.4 and right now we're trying to get rid of it so bad.