I cringe whenever I run into people who don't see the need to backup their files, or are content to do it only when they remember. What could possibly go wrong? Drives die. Power blips can scramble your data. Backups can fail. Disaster will strike when you can least afford it. For this reason, you really need multiple backups.
This fact has become very apparent on two occasions in the last month. Now, I don't know if it's a problem with Time Machine, or just a coincidence, but I've had both of my Time Machine drives (iMac & MacBook) become damaged to the point where I had to reformat both drives and start from square one. Not even my trusty old DiskWarrior could fix them. I noticed a problem with the first one when I tried to replace a corrupt file on my main drive by going back a week. No good. Back two weeks. Nope. Kept getting a message that I didn't have sufficient privileges, but no offer to authenticate.
Tried to repair the drive with both Disk Utility and DiskWarrior, and both kept hanging. Reformat time, and now all seems to be well. Fortunately, I have another drive that has daily backups of my home directory and documents folder. DéjaVu handles those daily backups, and has never failed me. And, of course, I use SuperDuper! for full, bootable, cloned backups. Multiple backups saved the day.
Last Friday, I discovered that the little Hitachi drive I use for Time Machine with my MacBook had been accidentally disconnected. When I reconnected it, it didn't want to mount on the desktop. Again, repairing it didn't work. After trying everything I could, I gave up and erased it, intending to start a fresh backup. After erasing it, I decided to run diagnostics on it and received damage errors. I had just about decided that the drive was toast, and was even checking warranty info, when I decided to give it one last try with my iMac. I have no idea why, but connected to the iMac, I was able to reformat the little beast, and diagnostics said it was a-ok. I hooked it back up to the MacBook, and all seems to be functioning normally again, although I'm seriously considering using velcro to attach the thing to the MacBook in hopes that the cable will not be knocked out again.
Backup drives are not expensive. Checking dealmac shows new bargains every day. Yesterday they listed a Toshiba 640 GB USB drive for $50. Need more space? They also listed an Iomega Select 2TB USB for $105. FIrewire drives are more expensive, but if you are on a limited budget, go with USB. Just make sure you back up those files. And remember, if one backup is good, two are definitely better. I know from personal experience.