I'm currently preparing to update the forum to vB4. I am currently working on the templates, and I will go over those a few times to reduce the risk of something being completely unreadable (I have found a couple of mistakes so far).
So, why not vBulletin 5? Simply because vB5 is riddled with bugs, and is lacking in functionality. So we will not upgrade to that version anytime soon. I have been helping out on a Swedish roleplaying forum that had changed to vB5, and the tech guy got burned out and went AWOL. So I'm currently uncomfortable experienced with vB5