As mentioned in a previous blog entry, however, the merging of GWT and Grails is not very straightforward and is subject to some idiosyncrasies, including the need to execute Grails commands from a terminal and not from within Eclipse. For some reason, installing GWT plugins from within Eclipse does not work (my theory has to do with environment variables but I just gave up on it and went with the sure-fire way).
The net effect is that GWT auto-suggest doesn't work. Nor does auto-creation of import statements. Bleh. I found that you can get the former to work fine by right-clicking on the Project name in Package Explorer, then Google > Web Toolkit Settings... You get the following screen:
Check "Use Google Web Toolkit" then auto-complete (at least) will work.