In the Cruising the Mall [WSJ]  article, it describes how you can shop on a cruise ship The Orphalese  in your spare time, and when you have had a enough, you can collapse in your own condo unit on the ship. Prices start at $1.8M with a model unit set up in their sales office in Las Vegas.
There are 200 condo units and 265 rooms for guests. Construction will be completed but condo units are available for sale now. The ship goes to a number of high profile events throughout the year [Luxist]. 
I assume they must be subject to property rights laws in the country of the ship’s registry. And financing? A mortgage? It would seem to be out of the question. Assuming the remaining parts of the ship are the common areas, its hard to conceptualize that there is no land associated with the residence.