Outdated templates are easy to fix because I remember all of the templates which I edit. Sure, there are a few each time to upgrade, but I'm not complaining.
It happened to me for each forum software that I used, when it's time for upgrading, haha.
But, I've always said I would suggest a way to find the changes that we've made in the templates. It'll be much easier to spot them when it's time for upgrading.
I hope that there will be a features like this when XenForo 1.1.0 comes out,