Ok.  I think I have 
Battlestar Galatica more or less figured out.  Here's my crackpot theory:
What makes the Final Five different from the other 
cylons is that they're from Earth.  This means, of course, that this new 
Galatica is handling time very differently than the 
original show, which took place in the (then) present-day.  If the new show takes place at least several hundred years in the future, then humans on Earth probably developed their own versions of 
cylons independently--although on Earth, they're probably called "robots."  And if Earth was significantly more advanced than the Twelve Colonies, these robots could be so 
sophisticated that they could easily pass for humans.  This would explain, in part, why four of the Final Five came to realize what they were by remembering a song from Earth: "All Along the Watchtower," by Bob Dylan.
Ronald D. Moore has, in the past, described the Final Five as the 
Cylon gods and suggested that they were immortal.  Immortality would be a very handy feature in a robot sent on a long-range space exploration mission.
Supposing I'm correct in this guess, the Final Five likely stumbled onto the 
Cylons shortly before, or shortly after the Armistice.  We know from 
Razor that the 
Cylons at that time were experimenting with upgrades to 
biomechanical technology.  First contact with the Final Five would have held the promise of skipping all the trouble and jumping right into the finish line.  (In fact, it's entirely possible the Final Five made a deal: the secret to biotechnology in return for ending the war with humans.)
The problem with this is that once 
Cylons upgraded to organic bodies, the old toaster models the Twelve Colonies made were obsolete, and needed to be retired.  The result was effectively a form of genocide.  This could potentially explain why the old 
Cylons in 
Razor were so pissed off at Kara Thrace.  If she is the final member of the Final Five, than from a 
Cylon perspective, she 
is the 
antichrist for helping created the new 
Cylons.
What this also would mean is that the 
Cylons never actually broke the armistice.  The machines that attacked the Twelve Colonies weren't real 
Cylons.  So in that sense, Kara Thrace is also the human 
antichrist for helping to create an army of zealots hell-bent blowing up humans.
Regardless of if I'm right in any of this, what is clear is that for whatever reason, the Final Five decided to forget who and what they are, and then concocted elaborate personal histories so they could 
integrate into human society.  Then, either at a 
predetermined date, or in response to a specific trigger, they came to their senses 
in unison.  To me, this suggests a plan.
One problem that needs to be addressed before the show ends is 
Starbuck: Why did she have those visions, why did she crash her ship into that gas giant, how is she still alive, and how did she get to Earth and back?  If I'm right about some of this, one 
explanation is that the visions were to keep Kara on track--to get her to do the things she needed to do, without having to remember why she needed to do them.  Like, say, killing herself. 
Let's say for argument's sake that the Final Five taught the 
cylons not only how to make organic robots, but also gave them the regeneration technology that allows a 
cylon's body to die and reawaken in a new body.  If that technology has a parallel on Earth, but with a much, much longer range, then 
Starbuck could have died in that spaceship, and then woken up on Earth.  Then it was only a matter of getting a new ship, finding 
Galatica again, and then leading them back.
Only time will tell if 
Starbuck is a good witch, or a bad witch, in the same way that only time will tell just how horrifically off-base I am about 
Battlestar Galatica.  (I shall probably never live down my fevered 
insistence that 
Snape would kill 
Voldemort in 
Deathly Hollows.)  That being said, I think this plot would make a 
cool ending to the show, and it also presents yet another possibility that really bakes my noodle:
I've so far been assuming the the Final Five are actually robots.  They could just as easily be what humanity has evolved into on Earth--not quite machine, not wholly organic, and functionally immortal.  If so, what kind of greeting can 
Galatica and the 
cylons expect to 
receive when they 
finally do get to Earth?
Oh, thank god I finally got that all out of my head.  
Ahhhh.  I am cleansed.  I feel so fresh and so clean.  Now I can finally think about something--anything--else.