My step-mother uses an old apple for her accounts and diligently backs up her work onto a zip disc. I've pointed out a couple of times that if the machine fails she'll have some difficulty finding anyone with a zip drive to restore her archive from.
What you don't realize is, as the tech guy, it is your responsibility to get on eBay, buy a zip drive, and load her backups
Already got one
I haven't told her though, I'd rather she upgraded, but I'm not completely daft.
While I'm here, I'll also comment on "BACKING UP TO MEDIA THAT HAS THE SAME RELIABILITY AS THE MEDIA YOU ARE BACKING UP IS NOT A BACK UP". A few years ago I had a 60GB un-backed up drive die on me. Since it was full of personal stuff I looked around the office (family business, had my PC there and it was full of bits and pieces of computers) and found another 60GB drive to try and rescue the dead one on to. A day or so later and I'd got pretty much all my data onto the second 60GB drive. "Phew!" I thought, "that was a close one!"
The next day this second drive died on me. A bit upset at my bad luck I had a look around the office and found a third 60GB drive and set about the rather grueling task of rescuing all my data again.
A couple of days later and the third drive dies on me. I rip it out of my PC and chuck it in a box with the other two... then I notice that they look the same. I have a closer look and discover that they are indeed all 60GB IBM DeskStars with sequential serial numbers.