etckeeper is a utility which keeps copies of your Linux (etc.) box's configuration files in a version control system. It ties into apt-get so each time you update/upgrade your system, your files in /etc are backed up. Which is nice. And of course you can request a snapshot of your /etc-files manually, before you start experimenting. Which is nice. Especially after you've munged your etc-file and stuff doesn't seem to work anymore. Been there, done that. xorg.conf i remember thee with pain.
As we use etckeeper here at work, i decided to install it on my home box. It was remarkably painless with a little help from a post from Evil Routers. I see no reason to repeat what's written there, so just follow the link. It's a five minute exercise and you'll be safe(r).
Now if i need to pick up the habit of always doing a cd /etc && sudo etckeeper commit before i touch an /etc-file -- or to find some mechanism that does it for me automagically :)