We are booked for an October 2005 cruise, knowing that we will switch our reservation to October 2006 once the dates open up.
For a seven day, its probably worth it, but you do need to have the deposit (I'm not clear if its $250 per stateroom or $250 per person - we did per person but I seem to remember you can do per stateroom).
For a three or four day, you only get the stateroom credit, and its smaller. You can probably get just as good a deal using your Disney Visa.