Are you doing JSR168? With JSR-168 portlets, you have the common APPLICATION_SCOPE that allows data to be shared with portlets in a common portlet application. Of course, that means all the portlets must be in a common war file.
You could cast the PortletSession into an HttpSession, and extract stuff like that, although you may find quirks going from one portal server to another using this method.
And of course, there's always the centralized database solution, although that's not always desireable. On WebSphere, I love the portlet/portal services that you can access and configure.
Ever though of accessing a Session
EJB? That's another option.
Good luck.
-Cameron McKenzie