hacker, you are a fan of Giger's art? I can see the beauty and expression in them, although at times I find them slightly disturbing. Your arm must be quite a sight.
Anyway, back to the topic. The discussion about how human we are, after replacing parts of ourselves, is an interesting one. Just to add to the confusion and as an example, do we consider patients with pacemakers fully "human", or cyborg? What about after surgeries involving body repairs made from animal parts?
On the intelligence side, which is a part of humanity IMHO, I tend to subscribe to Alan Turing's definition and idea of the "Turing Test", whether the subject being tested is fully or partly machine/human.
However, the complication arises because humanity is more than mere intelligence; without being too presumptous it probably includes traits like empathy, compassion, mercy etc, things that make us "human". If only there is a similar "Turing Test" for such traits, perhaps through test scenarios?