Here’s a few setups I’ve tried over the years that helped me stop worrying about backing up by automating the entire process.

Strategy 1: Just the basics

I used this system by itself for a while due to limited capacity on my external harddrive and still use it to keep an off-site backup of my most important files and documents. I don’t back up everything however, so bear in mind that this is a trade-off between storage-location security and capacity.

Basically I use Transmit and Automator to backup all some selected files to an FTP server. If you don’t have your own FTP server, you could also use a free dropbox or mozy account to do the same thing. Transmit installs a handy “synchronize folders” Automator action, so just select the folders you want to back up and save your automator workflow. Then you can use OS X’s built-in cron scheduler to automatically run your workflow to back up your files. (Edit: this guide (link) is helpful for setting things up!)

I usually back up my mail accounts, most of my application preferences, personal documents and files this way. Applications as well as my Photo, Music and Video libraries are not backed up though.

Pros: Offsite storage, access from multiple locations, no peripherals required.

Cons: The first sync could take quite a while, depending on the amount of data you’re backing up, although incremental backups after that are relatively fast. Longest restoration time as you’ll need to install a clean system and slowly rebuild your system piece by piece should your hard drive die. No backups of older versions of files.

Verdict: Ideally only used in combination with 2 or 3. Only rely solely on this strategy if you like reconfiguring your entire system or don’t have an external harddrive.

Strategy 2: Mirror your drive

This was my favorite strategy pre-Leopard. I used Shirt Pocket Software’s excellent SuperDuper! utility (Shareware, but offers a free mode that can also be used for this strategy – backups will take longer though) to create a complete copy of my harddrive on a partition of my external firewire drive (you can also use Carbon Copy Cloner, but I can’t attest to its reliability as I’ve never tried it). If a system update should break something, reverting to your previous settings is as simple as booting off the external drive and putting SuperDuper in “reverse gear”, copying your backup to your internal drive.

I set the external partition up to be the exact same size as my internal drive and ran SuperDuper 3 times a week. The best part about this strategy is that restoring the system is super fast and you can even boot off your backup drive and continue working should you need to.

Pros: Fastest “turnaround” time in case of a crash, fastest backing up, predictable backup size

Cons: No version control, requires an external harddrive, no off-site storage.

Verdict: Great alternative for Tiger users, or if you frequently like to switch hardware or test different OS versions.

Strategy 3: Backup everything, all the time

Of course, no article on backups would be complete without mentioning Time Machine, Apple’s system-level backup utility built-in to OS X Leopard.

Time Machine completely relegates backups to a background process that most users won’t even notice and allows you to really just forget about them. Time Machine will also back up multiple versions of files, allowing you to retrieve older copies of documents in case you’ve deleted something important. As it stands Time Machine is more or less an ideal solution for most users. Turnaround time is fairly fast, although you’ll need to copy your files back onto your internal drive before you can use the system, there’s no way to boot off a Time Machine drive.

Time Machine will consume a large amount of space on your external harddrive however, filling it entirely before it starts deleting older versions of files. One way to avoid this issue is to partition your drive, but as  harddrives have become so affordable, it’s probably worth investing in a dedicated large backup drive. Also, should you discover an issue with a system update, there’s no easy way to revert to your system’s previous state.

There are a few reasons you might want to go with Strategy 2 instead, (say you want to keep around an older OS installation on a spare backup drive to boot into, e.g. to test something under Tiger), but for a lot of users Time Machine will be the easiest backup strategy to go with.

Pros: Version control built-in, unobstusive, most extensive backups.

Cons: Backups aren’t bootable, there’s no built-in way to easily schedule backups for specifc times or intervalls, requires 10.5 Leopard, capacity intensive.

Verdict: Highest level of data retention, not quite as flexible or customizable as SuperDuper!

Conclusion
Personally I currently use a mix of strategies 1 and 3: Time Machine performs my main backups, but I use a  DropBox beta account for my most important “current” files and also backup my photos to my FTP server. Apple’s system updates also seem to be much more reliable and you very rarely hear complaints about a system update making something worse, so the lack of an easy “revert to previous system” with Time Machine is not so much of an issue.