It can be severe, and is frequently destructive. It is often associated with symptoms of temporal lobe epilepsy. This involves psychological counseling and other techniques to develop a healthy self-esteem and better psychological defense mechanisms. Borderlines think like borderlines - they've spent their entire live with instability and pain. Aggressively retraining with motivational books and tapes works - if the patient will do it.
Borderlines live in the black and white.
I feel very strongly that this disorder can be beaten. Untreated, it has a dismal prognosis. It's important to acknowledge the diagnosis, and fight for a better future. Denial won't make it go away. I've seen miraculous improvement in many borderline patients.