Brad3117 - what you posted about bipolar disorder is dead-on. Unfortunately, it seems that this thread was started with borderline PD in mind. As Psyclops pointed out, there has been some theoretical discussion as to whether or not they exist on the same continuum, but they are not the same.
In any case, my understanding of the empirical support for DBT is similar to what has been posted - that it has been shown to predict decreases in self-harm, but not necessarily in overall affective instability. But those data are actually consistent with the treatment model - which promotes acceptance that the mood states are going to be there, and provides patients with alternative ways of coping when they experience significant dysregulation. So maybe the ultimate outcomes for DBT aren't overall reductions in mood problems, but rather better coping.
I have some clinical experience with DBT, and have found it to be useful in that it can provide patients with a new framework (e.g., through opposite action, wise mind, radical acceptance, etc.) to cope with their symptoms and functional impairment. But it does seem tough for people to implement when they are in crisis.
As for meds, I thought I'd post this abstract from a chapter that I have found to be useful:
From: Soloff, P.H. (2005). Pharmacotherapy in borderline personality disorder. In J.G. Gunderson & P.H. Hoffman (Eds.), Understanding and treating borderline personality disorder: A guide for professionals and families, (pp. 65-82). Washington, DC, US: American Psychiatric Publishing.
(from the chapter) The recommendations for pharmacotherapy in BPD presented in this chapter are derived from review of the existing empirical literature, consensus among members of the American Psychiatric Association (2001) practice guideline work group and its reviewers, and my own years of experience in studying BPD. It is important to recognize that recommendations for pharmacological management are based on a relatively small number of studies. The American Psychiatric Association work group that wrote the Practice Guideline for the Treatment of Patients with Borderline Personality Disorder found only 40-50 published scientific reports on the drug treatment of BPD. This is a woefully inadequate database. Through this experience it has been learned that drug effects in BPD are modest and that residual symptoms are the rule. Medication does not change character and should be viewed as an adjunctive part of a comprehensive psychosocial treatment plan, which may include psychotherapy and psychoeducation. This section describes the medications used to treat each of the three symptom domains in BPD: cognitive symptoms, affective dysregulation, and impulsivity.