I think for the first post I will keep it simple.

Some key points of resources:
Borderline or Bipolar or both?
http://www.psycheducation.org/depression/borderline.htm
Demystifying borderline personality: critique of the concept and unorthodox reflections on its natural kinship with the bipolar spectrum - 2004 - Acta Psychiatrica Scandinavica - Wiley Online Library
Bipolar II, Mood Swings without Mania; Brain Tours; Stress and Depression; Hormones and Mood; and more...

These links provide a glimpse at the "other side" of this argument, the one that claims BPD is actually just a mood disorder and belongs to be under bipolar like it use to be.