My goddaughter (her first visit), my godmother, and I all share the same birthday and we went last year when it was free on your birthday. I realize the novelty of the 3 of us having the same birthday is something very special but we were treated like princesses the entire trip. CMs continually wished us happy birthday and acknowledged us, often doing double takes when they saw all our buttons.
The Dolphin upgraded us to a deluxe balcony fireworks view room and also sent us each an individual birthday cake. They also sent chocolates, champaign, an autograph book and Minnie pen and balloons. The trip was only booked 6 weeks out and we were unable to get ADR's for CRT but we thought we would check if there had been any cancelations as we were walking by (my 7 year old goddaughter was in awe of the castle). They said they absolutely had a table for 3 birthday princesses. We each received a card signed by all the princesses, were each given a special birthday cake with a candle, and they sang to us.
Peaches and Cream also gave my goddaughter a balloon and sang to her.
We weren't expecting anything other than our "free days" but it turned out to be even more Magical than any of us could have dreamed.