Efthimiou and Gandhi prove via a swift, neat reductio ad absurdum based on blindingly simple mathematics that vampires do not exist. They also polish off ghosts and zombies, though with less panache and more physics. (via)
Later: On second thought, I'm unhappy with it. Everything is based on the eat-once-a-month = reproduce-once-a-month thing. Buffy aside, literary and cinematic vampires (Lestat, Dracula) eat often but create fledglings much more rarely. Vampirism may be sustainable after all.