We purchased a backup drive for our household about a month ago. My wife has a Mac Mini and we bought the matching LaCie 250GB drive.
A couple days ago, Amy started noticing some problems with the Mini. It degraded quickly into not being able to login. I tried everything from running diagnostics to reinstalling OS X. No luck.
I made a trip to my local Apple store to give them a chance to take a look. They quickly declared the hard drive dead and replaced it.
Enter the backup drive. My wife is using Backup (need active .Mac account). All we had to do was hook-up the firewire cable between them and restore the files. It took some time (about an hour), but it was as easy as pie.
Backups use to be for servers and geeks. As more of our life ends up on our machines, we need to take precautions.
Go get yourself a external hard drive and a buy a recommended backup program. You will not regret the decision.