We recently acquired JavaWorld and are right in the middle of bringing the site over to our existing server farm and content management system. Tons of good stuff on the site, but for me, one of the cooler parts of the site is the forum area, which I've been happy to see is quite active.
Alas for me, it runs on UBB. There's nothing particularly wrong with UBB that I can tell; it's just not something I've ever used before (oh, joy: another template system to learn) and the current setup is several versions behind. Today, we turn off the forum so I can upgrade to the latest versions (in several steps, natch); should be interesting (it worked OK yesterday on a testbed, but, yes, everything's being backed up first).
Longer term, it would be kind of cool to migrate from UBB, which is PHP, to a Java forum like Jive or JForum (JavaWorld being, well, Java and all). But for now, well, UBB works (if you've used UBB and have any gotchas or cool tips, !)