Your suggestion to attach widgets to divs in page agrees with out experience. We use a static HTML page as a framework and hang the various active bits on it. No need for jsp since all dynamic content is handled by the GWT parts.

We also prefer to spread the application over a family of pages so it behaves more like a normal web site.

The secret to working this way is a good URL design - as in any good web app. To keep everything stateless and generally RESTful your in-page code must inspect the URL to get its context.