c/p http://danenet.wicip.org/dcccrsa/saissues.html

Healthy boundaries though not perfect, allow a person to experience a comfortable interdependence with other people, resulting in generally functional relationships and positive self-regard.

Damaged boundaries operate inconsistently and often dysfunctionally. They are the result of mixed messages and abuse, and are usually related to abusive relationships in the individual's family of origin and/or relationships of choice.

Walls protect the person who has constructed them but do not let anything in or out. This person lives in a state of loneliness, possibly protected from the assaults of others, but also prevented from establishing trusting and intimate relationships. People with walled boundaries have generally been deeply hurt by others and have erected barriers to prevent being hurt again by others' actions, thoughts and feelings.

No boundaries is the opposite extreme from walled ones. A person with no boundaries is unable to prevent unwanted intrusions and may be unaware that it is possible to do so.