Ah, Blade Runner.
The new "final cut" edition, and the various featurettes contained on the various DVD sets of it, have brought the old question of "Is Deckard a replicant?" back to the fore. I first noted the new wave of discussion at The new-er-est "Blade Runner" by Jim Emerson. The fourth disk also contains a documentary specifically on the subject, "Deck-A-Rep: The True Nature of Rick Deckard".
In it, both director Ridley Scott and Jovanka Vuckovic, editor-in-chief of Rue Morgue Magazine, make rather simplistic and patronizing cases for Deckard being a replicant. Frank Darabont makes an excellent case for Deckard's humanity, however he loses a couple of points for his insistence that the story falls apart with any alternate explanation.
The documentary wisely finishes with Paul M. Sammon and his conclusion, "Maybe."
The best response to the issue, however, is found on the second disk, in the documentary "Dangerous Days: Making Blade Runner". In that, original screenwriter Hampton Fancher says, "The question is interesting. The answer is stupid."
What's ultimately sad to me is that it's the kind of thinking that demands all questions to have a definitive answer is exactly what keeps Hollywood from making more wonderfully ambiguous movies... like Blade Runner.