Gosh, we like to rain on people's parades, don't we?
Whether a show has already aired or not, I think its good manners not to give away the details of the "plot". Anyone want to give away the identity of Keyser Soze, while we're at it?
Regarding the million ancestors thing. Apparently anyone with European ancestry is descended from Charlemagne, because the number of direct ancestors in your tree in 800AD is more than the whole number of people living in Europe at the time (or something like that). Of course we're not all descended from Charlemagne because there are doubles in your tree; look at the Queen and Prince Phillip, both descended from Queen Victoria, so their number of ancestors halves straight away.
The point of knowing who your ancestors are, IMO, is being able to picture what went on in your history, and make it a bit more realistic.