I've been using rsnapshot to back up some of our servers.
rsnapshot can be installed via Darwinports (or manually; it's only two files:, a Perl script and a config file) and works beautifully on OS X.
Even though there might be an issue when using ACLs I prefer having a copy of the data instead of losing all....
It creates hard links instead of copies of files that have not changed. This way incremental backups can be made where each copy in itself is self containing, meaning that it is a full copy that can be copied back in case of an emergency.
There's a good page on this subject to be found here:
rsnapshot on OS X howto