Here is the script I use for my nightly backups, network-wide, as an example:

---
#!/bin/sh

exec rsync -xPHa --numeric-ids --delete-excluded --exclude=/tmp \
--exclude=/var/tmp --exclude=/sys --exclude=/proc --exclude=/dev \
--exclude=/var/cache/edb --exclude=/var/db /* \
rsync://selene.nvanc.ectrolinux.com/backups-entro
---

Please note the -x option, which instructs rsync to skip network-based 
filesystems. This command can only be run as root, and will create an 
identical copy of a local filesystem on the backup server: files that have no 
business being backed up or that would only waste disk space needlessly are 
excluded (/usr/portage should be in the exclude list above, however it's 
automatically excluded by the -x option on my machines).

Steam encryption and compression can also be worth-while, depending on the 
environment. Typically, encrypting the stream is a good idea, which is 
something I plan to implement on my own systems within the next few weeks. My 
network can happily throw around large amounts of bandwidth, therefore I 
choose not to waste extra system resources by compressing the data as it's 
being transferred.

On the server end, the applicable portion of rsyncd.conf is as follows:

---
[backups-entro]
        path            = /var/backups/entro
        list            = false
        read only       = false
        use chroot      = true
        uid             = root
        gid             = root
        hosts allow     = entro.nvanc.ectrolinux.com
---

I hope that provides some degree of clarification regarding one of the 
possible ways to implement a backup system.


-- 
Anthony Gorecki
Ectro-Linux Foundation