The Robot/Human Barrier

While reading through "why the future doesn't need us." I was struck by
a philosophical question that has bounced around in my mind for quite
sometime and returned in a rush, that is the question of what constitutes
idenity/living". This question was provoked in particular by the quote of Danny
Hillis. Hillis' quote read "I'm as fond of my body as anyone, but if I can be 200
with a body of silicon, I'll take it." This, in my mind, doesn't resound as being
alive in the truest sense or for that matter being the same person at all. While I
will admit that having the same physical body is not a precluding condition for
"being" I do believe that being a synthetic body with what was formerly my brain
does not constitute my continued existence. To highlight this
case further I'd like to propose a hypothetical situation. Imagine a
scientist were able to split a persons brain into two parts able to
function fully and independently(hardly a radical proposition) and with
retention of all the original persons thought, feelings and memories.
Then lets say that scientist inserted one of the parts back into the
persons previous body and the other into a silicon body able to function
"humanly". Which of these two new beings would be the original person,
Person A? or would there be any person at all? To clear up this question let me
postulate a furthering of the hypothetical question.
Let's say that person A and the new person, person B, were to diverge
from each other and inhabit two distinctly different places at the same
time. Then we must ask the question is it possible for one person to
exist at two different places at the same time? Almost certainly
everyone would answer this question with a resounding no. So this
person no longer exists as a previous person and instead is something
entirely different existing as something as yet undefined. I believe
this postulate highlights two things 1. a brain, by itself, does not
simply constitute a person for then both the original person and the silicon body
would be person A and 2. a person existing in a silicon body
may not even be himself at all and rather an entirely new person.
The second point in highlighted in that postulate can be further emphasized through
another postulate: let's say that person A decides that he will put his brain into a
robot body. All the necessary precaution are taken but by some mishap person A's
memories are completely erased although not other damage is suffered. Would this
new robot-persons still be person A? This new person has none of the experiences of
person A and never remembers being person A at all and may in fact develop a
completely different personality from that of the "original" person A. Say for
example person A formerly lived in a cabin in the woods never having very little
human contact before the surgery. When the new person A, robot-person, was released
they decided to release him into a large metropolitan area and he became an outgoing
socialite who worked regularly with other people, surely these two people are not
the same or even similar at all. They do not share the same physical body and they
have no overlapping memory. In fact the new person a never knew he existed before
the point when he reawoke form the surgery because his memory was destroyed. Does
this not mean that person A no longer exists and the resulting robot-person is a new
person altogether?
Although these questions a abstract in concept I believe they highlight an important issue. When dealing with the future when do we draw the line on what is human and what ceases to be human. Is a cryogenicly frozen person who reawakes and has lost his memories still the same person? At what point does a person with robotic part cease to be a person? I think these are question we must answer before we approach a time when these technologies are widely available.