Over at the Daring Fireball blog, John Gruber has a nice article about how his extensive backup saved him recently from losing data on a hard drive that died. I know the utilities he speaks of (SuperDuper and DiskWarrior) and can vouch for their usefulness on Macintoshes (although I prefer to use psync instead of SuperDuper).
It was Merlin Mann over at 43Folders who noticed the article and then wrote his own take on John’s article.
For Linux and Unix, backups are much more varied. Two of the most widely known programs are Bacula and Amanda, both enterprise-level backup tools. For personal use, I prefer to use rsync to make copies of my home directories. There are a large number of tools that use rsync to make backups; one tool is from Mike Rubel from way back in 2004, with a comprehensive article titled Easy Automated Snapshot-Style Backups with Linux and Rsync. Another good article is from Joe Brockmeier on Linux.com titled Back up like an expert with rsync.
One popular (and simple) backup program is Dirvish, which I believe uses rsync behind the scenes. I’ve used the KDE app keep before, which was an easy and pleasant experience. The program rdiff-backup is also commonly recommended.
Whatever you use, the most important thing is: do it! The easier and more automated the better: if you dread making backups, you won’t do it.
Also, don’t settle for just one backup: what happens if you need to retrieve a backup from a while back – or your primary backup system fails? Best is multiple backups with multiple methods: backup to another disk and to the Internet (using sources like SpiderOak or Box.net or even Ubuntu One).
Lastly, there are a couple of Java-based backup programs – specifically, Areca and plan/b. Cory Buford wrote about these programs for Linux.com in 2008; it is hard to see how Java-based programs can reliably read all filesystem attributes and restore them without problem. Java, after all, is available from HP for the OpenVMS platform; do these programs restore all ODS-5 attributes? Do these programs work with other Linux filesystems like XFS and JFS and ext4? Perhaps someone can fill us in…
Whatever the case is – whatever the tool – go backup your personal systems now! I know I will be backing up. Don’t wait until your data is lost.
UNIX Administratosphere 
For my Mac, I’ve recently set-up a semi-automated backup solution for myself using rsync and a little launchd magic. I cobbled together the solution based on two other articles/scripts written by David Gohara (http://www.macresearch.org/tutorial_backups_with_launchd), Aidan Clarke’s “bash-ed” version of Gohara’s tcsh script and an rsync script written by Matthew Phillips (http://www.egg-tech-com/mac_backup/)
My solution uses launchd to watch the /Volumes directory for changes, then launches a script that rsyncs my entire HDD to a specific external drive when it is connected, then “blesses” the drive so I have a constantly up-to-date *bootable* backup that, should anything happen to my internal drive, I can just rsync back to a new internal and not have to re-install OS X or all my software.
Thanks for sharing what you’re using, and for the reminder to always back-up your data.