To not lose your data I would recommend two things:
- Have two partitions: one for / and one for /home.
- Manage your settings with Git or whatever, and save them on another machine.
When you reinstall, don't modify the /home partition and your settings in /home will be kept.
However I also recommend to use Git for all the settings, including things you want to keep in /etc or /root, and push this on a remote server.
Using a configuration like this, I switched from Debian Unstable to ArchLinux recently without much effort.
I don't keep the old partition, so if the new distro does not work I need to reinstall something else.
EDIT: some details about how I manage my settings:
Basically, I have a dotfiles repository where I keep all my dotfiles (things like .vimrc, the .config directory, the .gtkrc2.0 file, etc), and I have a shell script that links all this to their path:
/home/sphax/.vimrc -> /home/sphax/.dotfiles/vimrc
/home/sphax/.config -> /home/sphax/.dotfiles/config
You can add whatever you want in it, but keep in mind that a lot of those dotfiles still have the default values, so you don't need to version the files that you didn't modify.
For /etc and /root you do the same, one repository for each, that you put somewhere on the /home partition and you symlink everything.
With a setup like this you also get:
- easy backup (just push on a remote server)
- easy sharing (for example I share my dotfiles directory across 3 machines, one Debian and one ArchLinux)
It needs some tweaking/code writing at first but after that it's super easy and efficient.