I think I addressed this at length in my LJ, so I won't rehash it here at the risk of annoying our hostess. But, in brief, what appeals to me about Deckard being human is that he's simply another kind of machine. A killing machine. Not literally a replicant, but in many ways less human than the replicants. The movie, to me, is about him regaining his humanity through his encounters with the replicants. The 'hints' sprinkled throughout the movie point up his symbolic replicant-ness, not his literal status as a replicant. So the problem I have with the 'he's a replicant' theory as advanced by Ridley Scott is that it makes it too literal.

As Rutger Hauer put it, there's more power when a replicant saves a human than if a replicant saves another replicant. As he also put it, it's about a man who wants to fuck a machine.