The soulless zombie (wikipedia: lacks a soul but is otherwise indistinguishable from a human; this concept is used to inquire to what, if anything, the soul might amount) is useful in that it illustrates the beliefs of many people. it symbolizes romantic/religious/human intuitions about consciousness. i don't think it's especially relevant to the philosophy of consciousness, but it is a useful construct.
Slashdotters would love the challenge of a neurological zombie: Could you invent a beautiful machine that has a living human brain driving it? And if you could, would there be a way it could not have consciousness? I think this zombie supports functionalism, and so do I.
The role of the behavioral zombie (wp: behaviorally indistinguishable from a human and yet has no conscious experience) is again as a useful construct that's not that philosophically relevant. Most nerds don't have much trouble imagining a replicant of their own demising that would be very hard to distinguish from a human, but wouldn't have free will or self-awareness.
The white elephant in the philosopher's office is that the study of consciousness will eventually become more of an empirical discipline and rely less on the linguistic false-distinction or the unrealistic thought experiment.