Google have pulisheda new article on the GWT site that discusses some of the benefits of hosting a GWT app in a dynamically generated page vs. static HTML. It's a common enough problem: you want to show your GWT-based app only to users who are logged in. In this article, we'll take a look at several ways to accomplish this with a preference for those that make efficient use of the network: Static host page with RPC; Security constraint in web.xml; Servlet as host page; Template-based host page.
A common solution is to call a GWT-RPC service in the onModuleLoad() method of your EntryPoint class to check if the user is logged in. This initiates a GWT-RPC request as soon as the GWT module loads.