Here is my 2 cents on this matter. I could be horribly wrong though…
I think the greatest problem with faith healing is faith, or the lack there of.
Jesus said that if your faith were to be as big as a mustard seed you could tell a mountain to fall over into the sea in it would obey.
When Jesus walked on the sea towards the boat of his disciples, Peter asked if he can also stand on the water with him, he got out of the boat and was doing fine for a moment but started doubting and began to sink. (Matthew 14:22-33)
Jesus did many miracles, even when his disciples were unable to heal someone he could. He had the perfect faith. He could command nature and weather, he healed all illnesses, cured the blind, paraplegic people were able to walk and he even resurrected people from the dead.
I think that praying for someone’s limbs to grow back would require allot faith. It’s like jumping from a 15 story building and trying to believe that you’ll land on your feet without a scratch. You jump, the moment you realize that the ground is coming at you faster than a speeding train, doubt sets in and you are in big trouble (kind of like The Matrix

lol!). No one I have head of had such great faith except for Jesus.
Never heard of anyone’s amputated limbs growing back on? Then have a look at:
http://healingsandmiracles.org/
http://usa.cagora.com/node/110187