CentOS 6 vm server with with Liferay 6.1x running on Apache Tomcat (MySQL) and another java open source application integrated via portlet JSR 286 specification. Setup is sandboxed, not in production use and no legacy data involved.
Portlet integrate openbravo 3x with liferay 6x with full , organisations, user, role synchronisation between both systems using CAS (SSO), LDAP including session management and authentication. Setup mules ESB and configure one web service call between openbravo and liferay to a registry or directory in liferay. The one web service call in this scenario is to test the plumbing between both systems and vice versa.
We would expect observance of the JSR specification and have already integrated into Liferay a java based open source ecommerce solution to JSR 286 specification and would expect same standards. We would suggest using JSF,seam richfaces, icefaces, portletfaces, bridges such as seam, weld, jsf, struts, Apache Pluto and seam test for evaluating your portlets before integration. Integration between both systems must allow inter-portlet communication and minimise Ajax latency issues.