What are the Daleks up to? I think we've been focused on the Doctor and Donna so much that nobody has really said much about this. They're building something, it needs loads of humans and a load of planets, all to be turned into some sort of mechanism.
They've already re-created the Daleks so it isn't for that. So what is it, and why? And what is the Dark that people keep mentioning?
The only answer that makes sense to me is a doomsday machine - they're building something to wipe out all non-Dalek life in the universe, possibly by changing the cosmic constants to make the universe inimicable to life (see School Reunion) or snuff out the stars. They're planning to survive this, of course, possibly by being that vital second ahead of the rest of the universe.
Anyway, that's an answer that sort of makes sense to me, especially because if it involves large-scale time manipulation it gives an escape route for the Doctor and Earth. I still don't know Donna's place in this; I think she might be the Key to Time, but not sure.
Any other ideas?