In the corner of my living room sits a Western Digital My Book World Edition II.  It's basically two 500Gb hard drives plugged into a 150MHz ARM processor running Linux.  It acts as my file server, and I have Subversion running on it too.  The drives are configured as a mirrored pair, so all the data is instantly backed up.  I can access it from my laptop, or using a Samba client on my phone.

One former colleague of mine thinks I'm living in the past.  The Cloud is the way forward.  Information stored on proper servers with proper administrators.  Information you can access from anywhere.  Information you won't lose if your house burns down.

This is all very cool, especially as I think mobile technology is very cool, and Cloud computing fits very well with that.  It means you can do everything you need, without having to have terabytes of storage in your phone or netbook, without having to have huge amounts of battery-draining processor power, and without having to have an air-conditioned room to keep all your servers.  You can reach a point where you can do your entire job, using a smart phone while sat in a coffee shop.  And not see that as being "out of the office", because you don't have an office.  And that is cool.

Now, call me a control freak, but where my personal and business data are concerned, I do like a certain amount of control.

• The majority of gmail's 150 million users lose service due to a system upgrade.
• Microsoft's Sidekick service disrupted for more than a week, resulting in loss of users' data, again as a result of a system upgrade.

Now, I'm not suggesting that the companies concerned necessarily did a bad job.  Upgrades are usually a point when services must be temporarily suspended, and are a great opportunity for things to go wrong.  Sometimes, hideously wrong.  That's true of a private system as much as a public one.  The difference with a private system is that you can decide when to upgrade.  You can choose not to upgrade, for example, during the last week of a project, or in the middle of a sales presentation.  At the very least, you'd like to know in advance when an upgrade is going to happen, and have the means to plan around it.

You're also at the mercy of your service provider in other ways.

• Dashwire (a cloud service for Windows Mobile users) withdraws service, due to changes in their business model.

They might change their business model, and stop providing the service you currently use.

They might decide to withdraw support for the platform you use.   Or, the other way around, the range of platforms the service provider supports may limit your choice of platform.  For example, in a commercial choice guaranteed to alienate many potential business customers, Dropbox supports an iPhone client, but no client for the more popular platforms like Symbian, BlackBerry and Windows Mobile.  Many services might seem platform-neutral, providing access through web browsers.  But at what point will these add some feature (probably a cosmetic feature, which you didn't want anyway) that relies on some new scripting feature that your browser doesn't support?  Assuming the service works through your browser in the first place, that is.

Then there is the issue of security.  Personally, if I discover that any of my friends or colleagues are using Google Voice, I won't be leaving them any voice mail.

Before considering a Cloud service for anything really important, there are certainly some questions I'd like to ask.

1. Is there any Service Level Agreement?  If the service is free, then probably not.  If you rely on a free service (particularly for a business requirement), then you're asking for trouble.
2. Can you get all the data back from the service?  Can you get it in a format you can use, say, to transfer to another product?  Remember that they might lose your data, they might withdraw the service, or you needs might simply change.
3. Is this service the provider's speciality, or do they have another agenda?  How important to them are you as a customer?  Do you want to entrust confidential information to a company that specializes in web-searching or social networking (basically, in making information more accessible)?
4. Where is your information going?  Geographically, I mean.  Is it covered by the data protection laws you're used to in your home country?

For now, at least, my NAS and my smoke-alarm are keeping my data safe...