Steve Riley's recent post links to a Myth Busters demonstration of three different techniques to beat an "Unbreakable" biometric door lock.
I presume that the best practise advice from the lock's manufacturer recommended including a form of authentication such as a PIN to compliment the biometric device.
The Mythbusters video itself is pretty compelling - the link's on Steve's post.
Even when used as a form of IDENTIFICATION it's necessary to ensure a controlled environment whereby the individual actually presents a valid identifier. With the exception of passport control it's unlikely to make sense for a human being to observe each use of the device to ensure people play by the rules. Human beings are fallable too but perhaps I should stop there...