OK, so I've just had a great idea.
Consider Cyril, who I've been in sporadic touch with for the last 10 years or so. We'd like to think that we were friends, but as we live so far apart, we only see each other every 10 years or so, and the rest of the time we phone or email.
Cyril has lots of photos (3Gb) that he'll never want to lose. He's backed them all up to an external drive, so if his main hard drive breaks, he'll still have the photos. However, if a Cessna 172 falls onto Cyril's house, and breaks both drives, he'll have no photos. He might just get round to uploading them all to an ftp site somewhere, but in the mean time, he needs a backup buddy.
What Cyril does is put all his photos in a password-protected zip file (so I can't sneak a peek), burns the zip file onto a DVD*, and sends it to me in the post. When I get the DVD, I'll check that I can see the zip file, and then put the DVD in a safe place. As I live 218 miles away from Cyril, when the plane lands in his lounge, the DVD won't be damaged, so I'll send him a copy for when he's found a new computer (and house. And plane).
Clearly it's not the most robust solution, but it's a quick and cheap way for storing data that won't change.
As it's my idea, I'm prepared to be a backup buddy for up to 5 people. If you'd like me to keep a DVD or two safe for you in Uckfield, East Sussex, UK, then send me an email.
* Or a pen drive, or whatever.