My friend and I stayed at AoA in February. We were assured at check-in that we could set up our magic bands so that her charges would go on her credit card, and my charges would go on mine. We each had our own individual PIN numbers.
I had read on the DIS that other folks had had problem keeping their charges separate when staying in the same room, so I checked at the front desk to see if it was working. It was not! All of the charges were going under my friend's credit card, because she was the one who had made our resort reservation (which could really have been a problem since, once you reach $500 at a value resort, they charge the card!).
Luckily, they were able to tell whose charges were whose, I suppose based on the PIN numbers from the magic bands. They manually separated out my charges to my credit card, one by one (took about 15 minutes). I was assured that, going forward, each of our personal charges would be separated out onto the correct credit card. I was still nervous about it, so stopped by the next day to check again. Same problem! They straightened out our charges again, and from that point forward, I stopped charging things to the room. It was just too much of a hassle to keep spending time fixing the problem!
It's such a shame, because I really liked the convenience of using the magic bands for charging things!