In Russell T Davies Production Notes column in the new issue of DWM 404, he talks about the dangers of shooting on location and subsequent spoilers. Russell mentions that sometime in April they'll be shooting something which will probably be the biggest spoiler since the series returned!
He closes with But some of this is going to be big stuff. Really big stuff. Really, really, really big. Like, massive. Genuine Doctor Who history is waiting at the forge to be hammered into shape.