Microsoft subsidiary Danger last weekend suffered a catastrophic server failure that has led to the loss of personal information by some users of the T-Mobile Sidekick, a cell phone and personal communication device. And it dramatically underscores the shortcomings of trusting all your data backup exclusively to so-called “cloud” services.

Before the iPhone’s release, the Sidekick – sold by cell carrier T-Mobile in the United States – reigned supreme as the hip online gadget carried by celebrities and young people who wanted to stay in touch. A clever rotating screen and QWERTY keyboard made the Sidekick a popular accessory for more than a million users. Microsoft in 2008 acquired Danger, which once attracted Apple co-founder Steve Wozniak to its board of directors, for half a billion dollars.

But the Sidekick has a fundamental flaw: Users have to trust their data to the cloud. There’s no mechanism for Sidekick users to synchronize data with their computers, as there is with the iPhone and most other smartphones.

T-Mobile depended on Microsoft’s Danger to maintain backups and archives of that data. Danger didn’t, so when its servers went south, that data was lost, and the initial indication is that it’s been lost forever.

Not all Sidekick users have been affected by the problem. But those who found the information lost from their device are unlikely to get it back, especially if they try to reset their devices.

First and foremost, this is astonishingly, astoundingly bad systems management, to be sure. Microsoft and Danger, and by extension, T-Mobile, have absolutely no viable excuse for it. T-Mobile is now attempting to ameliorate angry customers by offering them a token credit, but the damage is done, and there’s bound to be a mass exodus of users who aren’t willing to give them another chance.

Cloud computing isn’t a bad idea. It holds the promise of ubiquitous access to your data, whenever you need it from, ostensibly, whatever device you have access to at the time. That promise, and customer demand, has led to a veritable avalanche of cloud services that have erupted in the past couple of years. Everyone from Google on down has gotten into the act.

And despite security risks and access problems, cloud computing is more and more figuring into individuals’ and companies’ data access strategies. It looks like cloud computing is here to stay.

This is not a bad thing. What is a bad thing is trusting your data to the cloud alone. Any backup strategy worth its salt should involve as many levels of redundancy as you can afford and manage. In cloud computing’s case, you should consider your bare minimum level of backup to consist of two layers: local and remote.

Sidekick users aren’t to blame here. Danger and T-Mobile haven’t given them any other choice. But this should serve as ample warning for everyone else.

Danger isn’t the first cloud computing company to lose data, and there have been other examples of cloud services companies that have gone out of business or abruptly changed their business model and suddenly left their users out in the cold.

So don’t be a sucker. Don’t depend on the cloud to save you. Clouds are, by their nature, transient things. Make sure to keep your own data safe by employing and diligently using a cogent backup strategy instead.