I actually went to the JP event last night because I happened to be on the test server at the time. The group I was in lost heartily, but it was still fun. The chamber we went to had 3 HNM types mobs, a KB type behemoth, an Aspid-sized adamantoise and a perpetually flying jorm/isgebind. We had 36 people but no one knew what to expect and our jobs were pretty random.