I'm a bit miffed about Dumbledore apparently knowing about the requirements for Voldemort to cast the spell to restore his body. That wasn't part of the prophesy, that was, in the original canon, magic of Voldemort's own creation. Even if Dumbledore knows Voldemort to be capable of such a thing, he shouldn't know how. One difficulty of compressing plot elements from a series that takes place over seven years into a one year space is that you have to be extra careful that people don't suddenly start knowing things they shouldn't know.

I would expect this would be a well-known spell to anyone who knows about horcruxes (at least, knows about it to the point of either actually using them, or opposing someone who does). Am I forgetting some reason why it wouldn't be?

EDIT: Oops, I guess this comment is obsolete - I misread the "old piece of dark magic" edit.