I'm not a neuro-scientist by any stretch of the imagination, but surely I'd think that you could only fit somehwat same-age brains into about same-age bodies? When I say 'around' the same age, I'm reffering to a tops 20 years gap, between people of which the oldest would be around 60.
I don't think this would ever cause anyone to be able to extend their life through the use of new bodies, at least not on a huge scale, because you have to remember that this person would have to 'bring' his/her brain along for the ride every time, and that on it's own sounds quite risky to me. Then there is the psychological impact of someone creating a new identity every 50 years - How long would it be until you start forgetting who you once were and where you came from? Already around the age of 30-40 the average person will start to forget about their motives and the factors that shaped their identity in their early-to-mid teen years, simply because you've already overstretched your brains capacity for information at that point.
You also have to keep in mind that the brain, like any other organ, has an infant stage, evolves, matures and eventually, deteriorates. Anyone who would be at risk of amnesia, or other mental disorders that can be caused by brain degeneration, would probable still come to suffer from these issues, and one day the brain would simply stop functioning: It's not made with 200 years of use in mind.
I don't know - This is more me trying to fit it all in my own head, before someone takes it over, and I'm not a scientist, to please don't harass me if some of it doesn't add up. I've studied psychology at a medium level for two years at one point, so I can back a bit of it up, but I'm not here to start a fight.
Anyways, my oppinion on the matter? I think, much like the creator of the topic, that the extremely scary part is the idea of entire bodies, with the brain about to be, or already, surgically removed, for sale on the black market like any other organ. I think this is a very real concern, and it would happen. There are plenty of people exploiting poorer coomunities around the world, stealing their organs, or indeed their bodies, in the case of human traficking/forced prostitution. Unless we can make it so that you cannot steal a person, then our world is not ready for this kind of science yet.
And how would you pick the donors anyway? You men and women who died of matters that did not take an extensive toll on their body? Or does the subject have to be alive during this process, in which case, can they just signs a consent form and give their bodies away for 'adoption'? Is it fair to the parents of a young and pretty girl, sadly deceased, to have the risk of bumping into their -actual- daughter, in flesh and blood, but with some old hag's brain controlling it like it was a puppet?
I think this could open up wondrous opportunities, but those are outweighed by the horrors that it could bring.