Financial statements signed by auditors aren't the only things that don't always deliver what they promise. Our society is awash in technologies that aren't as reliable as people tend to think. Sure, it would be naive to demand that our innovations perform perfectly. But consider the following. In courts, fingerprints are a primary tool for separating the guilty from the innocent--even though nobody knows for sure how accurate fingerprints really are. On computer networks, firewalls are supposed to protect us from evildoers. But they may actually increase vulnerability by instilling a sense of security that the technology can't remotely guarantee. The predictions of computer models can be way off target. And after 15 years in development, HDTV is still the future that never comes. We should know the limits of current technology before blindly embracing such next-generation concepts as national ID cards. Examples of technologies that merit a skeptical review are listed on the right.