Having a film degree, we studied this awesome film in school. I don't remember the details now, but Deckard was originally intended to be a replicant. The scene in the kitchen was the one that was the giveaway in the film...his eyes glowed slightly and you really had to look to see them, as was mentioned above. The reason for the change to him being human escapes me now...
I'm thrilled that this version is coming out, though. It's one of my all-time favorite films.