The previous backup strategy had been to create LVM snapshots on the target machines of the various filesystems, mount the individual snapshots on the filesystem, and then back up the files on the mount point. There was quite a bit of scripting complexity to create and mount the snapshots safely.
As far as I can tell, the advantage of using a snapshot is that rdiff-backup won't complain that files may be actively changing while the backup is in the process of being created. (If someone thinks of other reasons to use LVM snapshots then please comment.)
What using the snapshot does not address is the fact that many applications cannot be backed up directly. Backing up certain application files directly may be reported as successful but would, in fact, yield a corrupted backup. In other words, the backup system backs up the files successfully but then they are not able to be used by the application when they are restored. The client has several applications that fall into this category including: Oracle, PostgreSQL, Zope, Subversion, and others.
So, the next task is a system administrative one of dumping application data, backing up the dumps, and excluding the underlying source files. First up...PostgreSQL.