some Debian system files for reference

[machiner]

See the article at the site: debian system files

[machiner]

You might also want to think about files and directories in your ~/ directory (home).  .gnupg, .opera, .mozilla, .bashrc -- these are things you probably want to have backed up.  Maybe you have a bunch of scripts for Nautilus, so save .gnome2/nautilus-scripts, too.

What about your mail directories?  Maybe you use Gringotts and keep your grg file in the .gringotts directory.  Keep sharp about your hidden /home/you files and directories.  Every once in a while burn them to a disc, label it, and file it away.

If you're setting up and running a server you already know the configuration files to back up, hell, just tar /etc and call it a day   With so many easy and reliable backup solutions you may wonder why I recommend having a working copy of typical system files around.  Well, they can be handy, and not bad to have when you're rebuilding your system  from scratch either.

Being able to do: mv /etc/fstab /etc/fstab.old, cp /home/you/systemfiles/fstab /etc/  is pretty nice.

For a quick restore using files instead of an image or similar I have on hand:

/etc/fstab
/etc/hosts
/etc/apt/sources.list
/etc/network/interfaces
/etc/resolv.conf
/root/.bashrc
/etc/profiles

After I reinstall Debian I just rename the existing versions and cp my versions in their place, et voila!  'Course, I gotta make the directories in the /mnt directory.

[xplozion]

Yep those are very important to backup if you want to feel like in your old system in your new system 

Also if you run other programs, for example rtorrent, dont forget to backup rtorrent.rc config files and such.

Another that might come handy is your xorg.conf too, sometimes i make so mane changes to it that i save a backup in case i re-install my system for whatever reason.

Another thing i i do alot is backup the bash_history files!! Yes  for root and for my user! I really find it handy and you can make a script out of it to make your life easy.

I build a script to install lamp server, download and compile rtorrent and libtorrent also to install it and to wget the config file and place it, and to install screen and make rtorrent run in a screen mode so it stays running in the BG

I learned this the hard way, while still a newbie to linux i often tested several distros, so after every new install i had to make all this stuff over and over, then i was like hey! i can make a script out of the history so it auto install everything for me: 

Oh well i just find it usefull... But thats meh!