I run raspbianRaspbian and use dd and cron to do automattedautomated backups of my SD card to my external usbUSB drive.
ReallyIt is a really simple solution, it. It runs once a week at 2am2 am on a Monday morning and makes an image of the SD card.
I wrote a script which shuts down services such as lighttpd and cron, to minimise the risk of the sdSD card being written to in the middle of the backup, it then calls dd, before starting to the services again when the backup has finished.
IveI've put the script and some instructions on my blog, http://www.stuffaboutcode.com/2012/08/raspberry-pi-auto-backups.html