Haven't done it, but you can read about others on the Weddings Forum. You probably got the scoop that it costs $1000 or so. You get married during the "At Sea" day(s) in one of the lounges (can't remember which one). They have someone play piano, you get flowers, a cake, and the vows are given by the Captain.
They will do your Palo reservation for dinner (included) and I think there are other immenities, but can't remember.
Unfortunately, my hubbie nixed the idea (15 years' anniversary!) ARG! I had to settle for the REAS. He just wasn't up for a formal event (or at least getting really dressed up).
So, good luck to you. The vow renewal on the cruise is WAY cheaper than the ones at DW.
Hope that helps. Wish he didn't nix it! We'll be on the Dec. 19th Wonder!
d