I've just had a bad experience with SBS2008 backup which failed to backup and restore the Active Directory (the NTDIS.dit file wasn't restored). Given the importance of this file, I now regret not backing it up independently, using a file-based backup with multiple levels of redundancy.
Going forward, which files in SBS2008 are so vital that they should be backed up?
<edit>In case it wasn't clear from my question, the backup/restore which failed wasn't just a backup of Active Directory, but a full system backup using SBS2008's built in backup. I want to know which files I should back up in addition to a full system backup.</edit>