In trying to use gravel in my project (on accord of wanting to use jBPM), I see that if I add the following to my faces-config.xml, the existing links on pages in my application do not navigate to their destinations. Clicking the links makes the user stay on the same page on which the link is clicked. By the way, these links are bound to methods in our application specific backing bean classes as oppossed to using gravel's n:nav in the xhtml page itself.
<navigation-handler>org.jboss.gravel.navigation.GravelNavigationHandler</navigation-handler>