I've not looked at the JVM options, partly because I'm unfamiliar with running them, and partly because it can be complicated to get them up and going on a shared hosting solution. I have run some other JVM rooted apps previously, when I was hosting everything off my Mac, but as soon as I started hosting things for other folks (mailing lists, mostly), I decided it was really time to host on more reliable (i.e., not likely to break because I'm screwing around with something else) systems. XWiki does look nice though, very clean, and an apparently very healthy developer ecosystem.