I have tried the walkie talkies a couple of times on a ship. They were (I think) the Motorola TalkAbouts. They worked, but the trouble was that everyone's was working. No free channels, and continuous conversation and/or static. I leave them at home now.
If I was going to bring them again, I would only use them for ship to shore communication while in port. Worked pretty well when I was in Grand Cayman one time. I was shopping close to the tender dock and the other radio was on the ship.
We us the 5 mile range ones with lots of sub-channels. I think they're COBRAs. We got a set of two with the charger at Walmart.
Celebrity Century 1/09
Carnival Destiny 10/07
Carnival Destiny 9/06
Monarch of the Seas 3/06
Carnival Inspiration 8/05
Carnival Miracle 4/05
Carnival Inspiration 4/04
Sovereign of the Seas 4/03
I caved in and brought them last time, only to use them the first day and pack them away. We have a good set with long range and sub channels, but as the others have said, too many others are using them at the same time. Also, they dont work between decks. I hadnt tried ship to shore though but unless the other person is close, I dont think it work well. We leave them home now. We have enough stuff to haul with a 5 mos and almost 4 yr old!