One of the things I disliked about vBulletin was that when you upgraded the software to a newer version, usually a lot of stuff would break. Template edits would have to be redone again, styling changes wouldn't always stick, templates sometimes would have to be reverted, and with vB4 mods more often than not would stop working altogether as well. I don't mind doing a few edits, but having to fix half my forum after each release gets annoying and a real time killer.
Is there anything you're gonna do to address these problems, to ensure an easier upgrade process? If so, how are you going to do this?
There are already an array of examples where one can see the attention to detail that XenForo has received thus far. This care and attention will continue and will be incorporated into processes such as upgrading.