In modern academic psychology nail biting is considered as a form of SELF-MUTULATION behaviour.

My suggestion to get rid of this unwanted habit is to become more aware of the psychology behind your unwanted habit. You can read more about the psychology of nail biting at:

The HandResearch Nail Biting Encyclopedia

By the way, many nail-biting persons get easily frustrated by their finger-behaviour. Feelings of shame are very common, however some people associate this behaviour with less common habits like e.g. canibalism! Nevertheless, nail biting can be quite harmless in case the behaviour is not accompagnied with physical injuries (like e.g. bleeding or painfull finger traumas).

What do you think of the psychology behind nail biting? And what is your experience and vision on this behavior?