If you used the alpha versions, configuration (and internals) has change a lot: only a few arguments are exposed directly as properties, others have to be passed as generic compilerArguments.
Another breaking change is that the plugin no longer links to a specific GWT version, which means that you now have to add an explicit dependency to gwt-dev. The plugin is automatically tested against the last two stable versions of GWT as well as the latest snapshot for the next version.
Also new and noteworthy in this version: preliminary support for dev mode, through a gwt:codeserver goal that launchescom.google.gwt.dev.codeserver.CodeServer. Contrary to the CodeHaus Mojo plugin, I built this with multi-module projects in mind. Note that, following the above rule, you'll also have to add an explicitly dependency to gwt-codeserver to your module.
Still no documentation (sorry), look at the integration tests and usemvn gwt:help and mvn gwt:help -Ddetail -Dgoal=<goal> to learn about the configuration properties.
I'll now work on updating my archetypes to use that new plugin.