Using
DVC points for a cruise is not a great deal, it takes a ton of points, which depends on what cruise, when and what category., and then when you start to think using points might be OK, you realise points are per person, not per room ! (For instance cheapest date and stateroom (cat11) for a 2009 7 day Eastern carribean cruise would need 276 points total for 2 people, and the most expensive date in cat4 would be 988 points total for 2) And unlike DVC rooms, cruise points needed usually go up each year
It is almost always a better deal to rent out your DVC points (actually you rent a reservation that you make with your points), and use the cash from that rental to buy the cruise ticket.
There are many that use points to cruise because it is easier, or they bought their points when points were much cheaper or "they're my points, and if I want to use them to cruise, I'll do that"
I also think that you can use points on one person, then pay cash for the other, but DVC does not publish the cash cost.