Well I personally don't think that DD's Dead and that Snape's a Bad guy. It must've been his plot to make Voldermort believe that Snape's yet loyal to him (What more proof, then to kill Dumbledore) and that his (Voldermort's) most feared nemesis is out of the way, so that Voldermort can come out from his hiding. If Dumbledore told his plans to anyone else, Voldermort could have known by occlumency, but Snape himself is an occlumens and there's no way Dark Lord can read his mind, so the plot is shared between the them only (remember the arguement Dumbledore was having with Snape, about something being very Dangerous and that Snape refusing to do it). And about snape, well he never harmed Harry. Infact, he protected him from the first year. Even in the end, Snape tells the Death eaters to leave Harry for the Dark Lord, making sure that he's not hurt. So I think its the Dark Lord who should now worry, not Harry.
