Ok this really depends what you use your machine for.
If it's just a desktop machine then backing up your home directory /home/username will be enough.
This will make sure you keep all of your documents, music, application settings, chosen theme and the like.
If you've been been installing services list apache, mail servers etc then I would advise also taking a backup of /etc also and cherry pick stuff to restore when you re-install. It's generally fairly obvious where things live (apache config lives in /etc/apache2, mysql config in /etc/mysql etc...)
Another thing you might want to do is to create a list of all the packages you have installed.
To do this do the following:
dpkg --get-selections > package_list.txt
Backup package_list.txt Then when you are ready to put ubuntu back on install as normal and do the following:
Ok this really depends what you use your machine for.
If it's just a desktop machine then backing up your home directory /home/username will be enough.
This will make sure you keep all of your documents, music, application settings, chosen theme and the like.
If you've been been installing services list apache, mail servers etc then I would advise also taking a backup of /etc also and cherry pick stuff to restore when you re-install. It's generally fairly obvious where things live (apache config lives in /etc/apache2, mysql config in /etc/mysql etc...)
Another thing you might want to do is to create a list of all the packages you have installed.
To do this do the following:
Backup package_list.txt Then when you are ready to put ubuntu back on install as normal and do the following:
It will then go off an re-install everything you had on before.
Hope that helps.
Copy your entire home directory (~/) and /etc. All settings should be in those two folders.
Also see Ubuntu, how to setup a new machine like an existing one