I used to spend a lot of time nagging people to back up their PC hard drives. Now I'm spending a growing amount of time telling them to back up their online information. It's great that users can now tap into so many services that exist in "the cloud" - which was a graphical representation of the old phone system, but is now used to stand for the internet. But the fact that your data is online doesn't mean it's safe.
Microsoft's Hotmail has been the great teacher. I can't imagine that any other web-based service has reduced so many people to tears. If you've never had the pleasure, Hotmail's most important feature has been that your email only survives as long as you log on every 30 days. Miss the deadline due to, say, a delayed flight, illness or simple forgetfulness, and Microsoft deletes your mailbox. If you had anything important in there, too bad. It's gone.
If you're still playing Russian roulette with Hotmail, then at least upgrade to the new Live version. This doesn't delete your email unless you fail to log on for 90 days. Better still, you can download a version of Windows Live Mail to your desktop. This will collect your email from Hotmail and other services, and save it on your PC's hard drive. So if Microsoft deletes the online copies, you haven't lost them forever. There are many other ways to lose your web-based data. A nice example was the chap who had all his email, his photos and a website with Yahoo, and some of these services were paid for. Sadly, he wrote something on Yahoo Answers that apparently violated the provider's terms of service, so they deleted his account.
A friend who took my advice and switched from Hotmail to Gmail also lost all his email, because he hadn't downloaded it with, say, Thunderbird. In this case, it's not clear if he just forgot his password or was hacked. Either way, his mailbox wouldn't let him in, and Google made him wait five agonising days before he could say he'd forgotten his password and answer the security question. Which he couldn't answer, as it happens. Oh, how we laughed.
And if you assume most of these software-as-a-service providers have foolproof backups, think again. If a service has 200 million users, spread over thousands of servers in various locations, it could have many terabytes of data and gigabytes of mail arriving in a continuous stream.
Taking daily backups is a non-trivial task. Sure, they could have operators stacking thousands of tapes in underground bunkers, but how much would it cost to find the bit of tape you need? If you are not paying anything for a service, it's best to assume that there are no backups, and that no one is going to provide any real personal help.
In fact, those are wise assumptions even if you are paying top whack. If you are wrong, you may get a nice surprise, but don't bank on it. Even cloud-based services that are reliably set up, well run and have great backups are not invulnerable. Companies go bust all the time. Your data ends up on the back of a lorry, destined for some other underfunded web 2.0 startup. You won't even get chance to bid it a fond farewell.
I think personal computing is wonderful, but hard drives fail and laptops get lost or stolen, so it makes sense to back up your data. I think cloud computing is wonderful too, but operators make mistakes, passwords get lost, servers get hacked, companies fail and so on, so it makes sense to back up your data.
As Schofield's Second Law of Computing asserts, data doesn't really exist unless you have two copies of it. Preferably more. And the only person who can be held responsible for that is you.