When Bill Gates and Ray Ozzie rolled out Windows Live and Office Live a couple of weeks ago, they didn't use the phrase "Web 2.0," but they did appear to embrace some of what that phrase embodies. The Live products are all about Web-based services that you can combine ("mash," in the parlance of Web 2.0) and/or build to create useful, even personalized, applications and output. What they didn't mention, though, is the same dirty little secret that most Web 2.0 proponents would rather you didn't think about.

That skeleton in the closet is what one developer termed the "drive-by upgrade." Writing on O'Reilly's Macintosh weblog, Fraser Speirs, a developer from Scotland, recounts what happened to his carefully crafted assemblage of information based on Google maps. Then Google "upgraded" the maps service, and the new version didn't interact with the Mac's Safari browser in the same way, so Speirs would need to redo much of his hard work.

Before you decide to roll out a new application or a new service for your users, you always (I hope) test it in the lab first. Then, depending on its potential for mischief, roll it out to small subsets of your user base, gradually checking along the way that everything is working correctly.

Even after all that, should a potential flaw be discovered it's relatively easy (if time-consuming) to roll back the upgrade or even reinstall the last-known good version of the application or service. Google wasn't going to do that for Speirs; would you expect Microsoft to do it for you?

It's not as if upgrades to Microsoft applications and services go smoothly, right? Just about every Windows upgrade in the past five years has broken something. Even changes to Microsoft Office applications can cause hardships as, for example, when a new format in Word isn't recognized by older versions.

While Windows Live and Office Live are targeted at home users and tiny businesses (those with fewer than 10 employees), the trend has always been for users to clamor at work for the same features they have at home.

It's not too early to be active with warnings to your users about the hidden pitfalls of Web-based applications that are beyond their (and your) control. Creating whiz-bang output is only good as long as you can read it. Betamax video and eight-track audio also were once the latest technology.