Any key or password can be replaced by a biometric system. In fact, anywhere you need to be recognized, to verify identify or prove that something is your property, a biometric system can be installed.
A common question is related to the biometric market, its existence and size. Well, most of the time, companies are reluctant to disclose numbers, especially when it is requested by their own customers. But Authentec is quick to make press releases, and the graph is summarizing their claims, which is a good marker of what is happening: in 2005, the market has really started.
Note that is not the total biometric market, this is only one fingerprint sensor manufacturer. Frost & Sullivan are expecting numbers like 500 millions sensors in 2010!
Have a look at my web site and make your mind. You will find a lot of biometric devices, especially fingerprints.
Many products are already using fingerprints.
Another big class, historically the first, is the identification for police application.
Now, some countries are using biometrics for immigration control.
Banks are now proposing some ATM (Automated Teller Machines)
Identification of the mother / newborn : systema ICN
Payment using biometrics is more and more used in stores.