One of the reasons I had trouble with Kim Stanley Robinson's really excellent novel Years of Rice and Salt was that the reincarnated characters weren't always identifiable as themselves -- their personalities also changed in each incarnation. And now I'm thinking maybe that was exactly the right way to do it: the soul may be the same, but the experience of reality -- and thus the way a person reacts to it -- is different.

Of course, if the soul only gets one shot at an earthly trip, then there's no reason it couldn't be formed by the experience of life rather than the other way around. Although I do like the firmware analogy... :)

Fun to ponder, anyway!