User blog comment:FoolishMortalFOOL/Devil Fruit Transplant/@comment-3242083-20110320125916

Interesting (and somewhat creepy) thought. I think nothing would happen.

1. Rule: A devil fruit power can not exist twice at the same time

2. Rule: The devil fruit powers reappear after death. So even if you would cut off Luffy's leg, the "dead" meat would loose its power (since it is going to respawn somewhere, or is still in the original user).

Of course there is still the big elephant in the room that is Blackbeard, but as Marco said...he is special.