Now that we're into the beginning of season 4.5:
1. The Gods and Humanity used to live together in harmony on Kobol.
2. Something -- I don't recall what, or did we ever know what -- ended that harmony. Humanity fled in 12 tribes (?) to the stars and founded the Colonies.
3. A 13th tribe left Kobol for Earth. We now think that 13th tribe was composed of Cylon humanoid models.
4. Kara Thrace's human body seems to have died crashing into Earth. The new Kara could be a Cylon.
5. In flashbacks to the beginning of Adama's first fights as a pilot (in "Razor" I think?), there was a moment when he discovered a Hybrid research station, reached into a tank, and was grabbed by something reaching for him. He was knocked back against the wall and fell unconscious. When he came to, he tries to save the "people" still locked in the station while a (hybrid's?) ship flees outside. Then he gets a radio notice that the war is over and that he'll be rescued.
Speculation:
A. Is Kara intended to be the beginning of the next iteration of Cylon models, a "refresh" of the set of models, as Cylons continue to attempt to replace Humanity in the universe?
B. After everything on Earth died (did it all die?), some other Cylon cell managed to stay or return there and maintain some level of fresh model production capability. Does that imply there's a hybrid or more in the wings there?
C. If Adama the young pilot was unconscious while the hybrid was removed to his ship, does that mean there's some Adama in a tank out there that we're going to see as another future model?
D. Were the Cylons the original Lords of Kobol? If so, did Kobol fail because of a revolution between the Cylon models that wanted to evolve and escape Humanity -- the 7 -- and those that were happy with the status of quo -- the final 5?
E. Since "this has all happened before and will happen again", does that mean we're looking at the rest of Humanity and the remaining Cylons forging a new home together on a new world, founding a "New Kobol", where they try to restart and improve their lives?