Just used it this morning for our stay next week. Used it the last two times we went. We DO NOT go during the really busy seasons and it has made a positive difference for us. We got taken care of more quickly, were given two options on the location we requested and got in the room earlier than they post. Now that was the Caribbean Beach and I know it's a big place and probably had lots of choices, but we even chose the village we prefer to stay in and got it.
I even asked the gal on the phone when we first made the reservations last year if it really made a difference and she said it definitely does. But again, we don't go when it's wall to wall people.