There seems to be quite a lot of confusion regarding integrating Maven with GWT 1.6, as Google has changed the layout to "exploded war" format. Which plugin are you using? Does it have goals for hosted/compile? Does it work "in place", writing output to src/main/webapp/WEB-INF, or does it use an external dir? (I'm not a fan of having GWT-generated output appearing in my source tree).
If you have something working, POM snippets would be highly appreciated as well.
I had this working by downloading the GWT Maven2 Starter App here and then changing the pom to use GWT 1.6.4 and it just seemed to work.
There's an article here about how to use GWT 1.6, the Google Eclipse Plugin, maven 2, and the gwt-maven-plugin all together.
I have updated the gwt-maven2-starter-app to use GWT 1.6.x and the codehaus maven-gwt-plugin. Their work around is to deviate from the maven convention and to use the 1.6 standard /war directory inplace (instead of src/main/webapp) for webapp artifacts and GWT generated output (which you should add to .svnignore).