Happy Deathly Hallows'eve
um, this is just a random thought- and i dont know if any1 else has considered it, but since Harry has stated that he's not planning on returning to Hogwarts in DH - though it wouldnt be HP without it - this might mean that DH wont transpire over the course of a full academic year. I doubt there is much JK could do to cover an entire year if Harry doesnt go back, so my bet is that DH is so called because the story ENDS on Halloween (when it all began - for Harry at least) - think about it, the deadly (Deathly) night on Halloween when Harry Potter vanquished Lord Voldemort for ever!