In the computer room at my college, many years ago, there was the following sign:
Rule 1: Always make a backup.
Rule 2: Always make a backup. (This is a backup of Rule 1)
Just because things are now on Web 2.0 services over the internet doesn't change the fundamental dictum. If you care about the data, it is you who needs backups. If you don't make backups, obviously you don't care (enough)...
What about Rule 0:
Rule 0: the following rules apply only to techies, who are the only people capable of understanding even the basic issues involved
Seriously, if you provide a consumer service of any kind, and you expect the consumers to do anything more than just use the service, you are seriously deluded. People - including, I suspect, many techies - will never do anything more than chat/download/email/surf/whatever.
My bank doesn't tell me to back up my account details in case their internet service goes down, why should anything else be different? Yes, that's a rhetorical question, and of course you and I understand the difference, but why should anyone else?
Anyway, the point is that this is not even a technical issue: it's a business one. How do you persuade people to start paying not only for "free" services (Facebook) but "worthless" invisible ones (a backup of your Facebook data)?
If you can solve that, let us know. Until then, going on about backups is only preaching to the choir. Most of whom have probably had a nasty experience with things going wrong already... :-)