I was just reading the article on the main page about the similarities between the Wraith and vampires, and I just had an interesting idea. We know in the SG universe the myth of Atlantis came from the Ancients who returned to Earth around 8000BC when they were fleeing the Wraith siege. Is it equally possible that the mythology of vampires also originally came from these same Ancients (who obviously knew about the Wraith)? Even more interesting, the Dracula legend was based around a real person (Vlad Tepes). Now, in real life he was not a vampire, just a rather sadistic person...but is it possible that in the SG universe that he could've been a Wraith that somehow made it to Earth? That would explain the Dracula/vampire legend in the SG universe even more.
Wikipedia article on Vlad Tepes: http://en.wikipedia.org/wiki/Vlad_tepes