to book a cruise using DVC points you have to pay a $95 fee ( non refundable). Points are high (in 2006 eastern cruise 7 night cat6 july 8th, 325 points each for the first 2 people, 188 points each for the 3&4 persons 13 years or older,
158 points each for the 3&4 persons under 6-12 years old.) the points go up ever year for cruises. you are better off renting your points and paying cash for the cruise. once you book a cruise and you cancel the cruise, you loose your $95 fee and you cannot use your points to stay a wdw dvc resort. you can use your points for
disneyland, wdw non dvc resorts plus you have to now pay another $95 to stay at non dvc resorts or another cruise w/another $95 fee or conceirge collect plus the $95 fee, adventure collection $95 fee.
you should check out the dvc board to get more questions answered if you have more questions, but this will help you with the cons.
the plus side if you use points, you dont pay any cash except the $95 fee and it would feel like your going for free