I read a theory on another board that Ellen isn't the final cylon, but rather an older version of Number Six.
It's a neat idea, but the BSG writers are so creatively bankrupt at this point that I doubt they would ever come up with something like that. I still can't believe how far this show has fallen.

I'll still watch it until the end in hopes that the finale redeems the past few seasons, but I don't think there's been an episode I've really enjoyed since before the New Caprica mini-arc.