There were some special Nickelodeon cruises on Roayl Caribbean a few years back. I believe they did 2 (one out of FL and one departing from the west coast) in each of 2008 & 2009. We went on the one in August 2009 aboard the Freedom of the Seas out of Port Canaveral. Nickelodeon basically chartered the ship for the week and it was pretty much a fully-themed Nick cruise. The entertainment all week was run basically by the entertainment staff of the Nick hotel in Orlando and was Nick-centric. The regular Royal Caribbean staff and cruise director ran very few of the week's activities. We had a great time on that cruise. They had game shows out by the pool every day, and lots of other Nickelodeon entertainment going on all day every day of the cruise. Everyone had the opportunity to get "slimed" - although it was really just green water. They only used the real stuff for their shows.
Towards the end of the cruise, the cruise director and the main Nick person "Reuben" (I've never stayed at the Nick hotel, but apparently, anyone who has stayed at the Nick hotel would know who he is) said that Royal Caribbean and Nick would be announcing the details of the next year's Nickelodeon cruises "very soon"...even hinting that it was a done deal but they weren't allowed to announce it yet. It never happened. Instead, a few months later, the partnership with Nick and NCL was announced where Nick would have a presence on a few NCL ships full-time, but didn't include any fully-themed cruises. RCI later responded with announcing their similar deal with Dreamworks.