We will advertise it more next week when people are back from holidays but we released the 2.4.1.SP1 (2.4.1 had a minor bug immediatly corrected in 2.4.1.SP1) of portal last week and it is available on sourceforge for those who are working with portal at the moment during the holidays, you can see that as a Christmas gift brougth to you by the portal team.
That release has a rock solid portlet cache implementation based on the render parameters, portlet mode and window state. More robust caching was requested by a couple of persons recently and we did listen to them.
Actually our caching layer did not have strong testing before simply because writing unit test case for that feature is certainly harded than writing the code itself (http://anonsvn.jboss.org/repos/portal/tags/JBoss_Portal_2_4_1_SP1/portlet/src/main/org/jboss/portal/test/portlet/jsr168/ext/common/AbstractCacheSequenceBuilder.java).
Now it is properly tested and we implement everything that is in the jsr168 specification.