As we have seen in this thread so far, there are plenty of Java-based CMS systems in existence. However, what Java needs is a system like phpnuke that allows a user to have the framework of a site created for them, and select a skin to suit your needs.
IMHO, there are too many small portal frameworks appearing, but no single framework has enough portlets to merit the time spent installing them. Other systems like Liferay are difficult to configure and require dedicated machines, i.e. you need your own server to have the amount of control and resources required. I think phpnuke exceeds in this regard because any man and his dog can download phpnuke, install it on his free/cheap hosting solution and have the capacity to included syndicated content, edit custom content, change skins at the click of a mouse.
Nukes is a positive movement towards a portlet-rich framework which allows a user to put a site together very quickly, with lots of functionality. My two concerns, though, are with the lack of an MVC framework (why didn't they bundle Rikard's webwork?) and the lack of portability.
What I would love to see is a portal system based on Struts/Tiles for the control and rendering, hibernate for persistence (perhaps Castor for XML) which would be installed in a sinle WAR file. I've been keeping an eye on http://jnuke.sourceforge.net/ for some time, but there seems to be very little happening there. Perhaps its a good thing that Marc et al. have started this project, it might spur some of us lazy developers to get up and do something about it, maybe join the jnuke project, just as Linus' move to bitkeeper sparked the bitbucker project!