There's been some discussion on the forums here:
http://www.virtualmin.com/forums/message-view?message%5fid=13706#13854
And in the writing of my posts, and reading Alan's response, I think I need to clarify my own understanding of how things work, and perhaps we need to simplify the way backups are done. More specifically, maybe there needs to be a way to specify a complete backup policy, including full system backup, domain backups, and configuration file backups, from a single location with a single configuration (i.e. destination, authentication details, etc.).
This is kind of a blue sky wish--I have no concrete idea of how things could be better than they are now, but there is a definite feeling I'm getting that things should be easier than they are.
I'm planning some useability testing sessions in the next couple of weeks and I'll add this to the list of tasks that a user should attempt. Once the analysis is done we may have a better idea of how things ought to work.