Haven't done it myself but : Check out the wedding and honeymoon forum. If you do a search you will find several descriptions. Most were highly complimentary.
If you contact Disney Fairytale weddings they are extremely helpful and informative. They are pretty easy to get through to on the phone.
I am sure you know the basic arrangements vow renewals are held on board on Thursday afternoons. They are conducted by the Captain. You get a choice of music and flowers. You get free concierge service. The on-board coordinator apparently is usually the head of concierge services. You get a cake and drinks at the ceremony, followed by dinner at Palo. You also get a complimentary rainforest spa treatment for both of you. You can have a photographer take pictures but the packages are pretty expensive and you dont get the negatives.
They also do wedding ceremonies on board!