Exporting data via a search syndication is probably a good thing in most szenarios (do we have something written up on that topic?), but for our use case we have two constraints:
a) Data exchange has to happen via webservices (I suggested using the Basecamp API for data exchange with the Project Manager, which was flat out denied).
b) We use a different Java based system for portlet display.
In an ideal world, I would just write Liferay portlets that query data using XML as you describe or the webservices and display the content. But... I have no intention to rewrite all the includes in project-manager, contacts, forums, file-storage, invoices and some selected ones in acs-subsite into liferay.
In the long run we are going to use the CAS server for authentication, so we can be sure the user is logged in (and auth::require_permission works). But that is a different topic.
