Checked into SVN head is the code that no longer generates the GWT callbacks that unwrap the parameter type, in favor of just exposing a parameterized AsyncCallback parameter to the Async service. This has simplified the generated code. Samples and documentation have also been updated. In order to support this simplification, Enunciate will no longer support GWT 1.4 as of release 1.15.
A lot of thought and investigation was done into supporting the use of the server-side types on the client-side. This was determined to be currently unworkable. The reason for this is because the Enunciate GWT module was designed to expose existing JAX-WS service endpoints as GWT endpoints. Since GWT and JAX-WS/JAXB have different rules and constraints on the objects and service interface, Enunciate had to provide a "mapping" layer between the JAX-WS endpoints and the GWT endpoints. The mappers that Enunciate provides to support this functionality rely on certain conventions in the GWT objects, and these conventions are applied in the generated code. Using the server-side types directly could break the mapping layer.