GWT 1.6 RC is out and a new feature shines: the new HostedMode is based on Jetty.

From the release notes:
“Although the legacy GWTShell still uses an embedded Tomcat server, the new HostedMode runs Jetty instead. There is also a new “Restart Server” button on the main hosted mode window. Clicking this button restarts the internal Jetty server, which allows Java code changes to take effect on the server without having to completely exit and restart hosted mode. This is useful when making code changes to RPC servlets, or when serializable RPC types are modified and the server and client are out of sync.”

GWT 1.6 HostedMode now using Jetty