When I was maintaining several servers for my university's, I always make it a point to keep tab of the server configurations for each of the services that we provide. One thing about using Linux is that it is sometimes a pain to keep up with the speed of improvements – yes, new stuff always keeps on appearing every few weeks and you'd be a fool not to check it out or try it.
In my case, I wait a couple of weeks before I apply the changes (to make sure that the new stuff does not break other important services). Sometimes, though, I just wait for all the changes to be incorporated into a new distribution – ensures that all packages are synced, i.e., working with all other services. The downside of this is the fact that you need to re-apply the configuration that you have done. I know that today it is just a matter of running apt-get but hey, I belong to the old school. :)
Now, thanks to Linux.com's Jeremy LaCroix for providing us with a script to make it simpler to back-up your servers configuration and then restore it after you have re-installed your operating system. Where was he when I was working as sys-admin? :)