I currently have a web application which acts as a Portal. Users log onto the Portal and are shown a list of services. To view a service, an iframe is populated in the same page pointing to the URL of the service. All applications are Seam 2.1.1GA on JBoss 4.2.2GA AS.
If a user loads up Service A, interacts with it, then switches using the menu in the Portal to Service B, interacts with it, then switches back to Service A and goes to interact, they get a ViewExpiredException (it's not actually shown to the user, I've got some code to display an error message rather than redirect etc.)