I seem to recall reading somewhere that clones of the same people could potentially have vastly different personalities. That said, I'm not sure where I read it (don't take drugs kiddies, they ruin your memory
), so as usual must appeal to our ever-beautiful board bimbo
Dr. Elegans for more info on this, if she can help.
I guess another point worth considering is upbringing, which plays quite a role in determining who we are too.