What to backup?

[jus71n742]

I am going to experiment with my laptop in doing a dual HDD system. Windows on one and Ubuntu on the other. If I want to do an upgrade while I am at it. 9.10 - 10.04/10.10 what all is essential to back up? just the home directory?
Am I correct in saying that it will also keep all my settings in place once I upgrade and restore? I essentially need to know this for when I do it on my Desktop with a similar setup but more scripts and such.

[s3MA00RRNY]

At minimum I would backup:

Home
/etc/apt/sources*
Firewall settings (location varies)
A markings list (load Synaptic. Go to File... > Save Markings)

Be sure to check save full state.

[Mark Phelps]

To be SAFE, you would also want to disconnect the Windows drive while doing the upgrade. This will prevent problems like changing the MBR on the Windows drive, or installing GRUB to a partition on that drive.

[jus71n742]

Well I have it up and dual booted. Windows restored correctly and everything is as I left it. Now the Ubuntu side I need to get my backup restored. I followed this
http://ubuntuforums.org/showthread.php?t=35087&highlight=backups

And when I restored and rebooted I still am missing some of the files. If I reinstall the programs with settings (Tbird, Chrome, etc etc) will they find the files or be a big ole maybe?

I only backed up /home.
and I am now up to 10.04 instead of 9.10 if that has anything to do with it.