After speaking with one of the guys running the Serenity demos, apparently the character advancement rules are intimately tied in with your ability to roleplay your character. You get these "plot points" during gameplay as a reward for good roleplaying (i.e. accurately portraying your disadvantages) that can then be used like action points/Force points/etc. to enhance rolls during gameplay. At the end of the session, leftover plot points are used for character advancement, though how I do not know.
I can definitely see whole campaign set in the universe, and I'm jonesin' to pick up this book.