We are running a clean install of Moodle 2.3.2 on CentOS 6.2, PHP 5.3.3 and PostgreSQL 8.4.13
In Backup General Defaults 'Include users' is on.
When running a manual backup (includes enrolled users) for some courses (but not all) the backup process results in a >1.4GB file. If the course is backed up with no users it is much smaller, typically 1MB to 30MB for most of our courses. The backup process runs normally, albeit for up to 20 minutes.
Inspecting the contents of the .mbz files shows all site users in the users.xml file and a huge quantity of files in the files folder. Why is this? The course definitely only has a normal number of users in it (2-45). I have yet to determine what triggers this behaviour, it does not happen for about 90% of our courses, but when it does it is a problem. It is consistent behaviour for a given course, ie if the course does it, it always does it.
We take end of course backups of all our courses before they are reset and keep these for up to three years. Working with backup files that contain all site users (and I think all their files) is not an option.
Richard