Here's what Mousesavers has to say about it (and I've also read this on the Unofficial Guide to WDW book):
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Postcard and E-mail Codes
For the past several years, Disney has regularly sent out masses of postcards (and more recently, e-mails) that offer deeply discounted Walt Disney World resort rates to the recipients. I can't publish those discounts, because Disney uses a PIN number system so that only the recipient can use the code. (When you call in with your PIN number, they match your name and address to it. You can't share the PIN with anyone else.)
So far in 2005, these postcards and e-mails have been the only source of discount codes for the general public. (In the past, there were a fair number of discount codes that were published widely in newspapers, etc.) I don't know if it's a trend, or if there are just fewer discounts available this year in general -- since tourism is doing better, it may be that Disney isn't seeing much of a need for widely-distributed discounts.
How do you get on the lists for these special postcards and e-mails? No one knows exactly, and believe me, I've done a lot of research on it. It appears that Disney's marketing department uses a variety of lists at different times.
If you want to have the best possible chance of getting these mailings, it's definitely a good idea to register with Disney.com and be sure to click on the boxes that indicate you're interested in Walt Disney World. You might also want to go to DisneyWorld.com and request a vacation planning video. It also appears that they may use mailing lists from Disneydirect.com, subscribers to Disney Magazine and Disney's Visa card members. In short, sign up for anything Disney (especially Disney World related) you can, and keep your fingers crossed!
If you are a repeat resort guest and have already subscribed to a lot of Disney lists, it's possible you have received a discount e-mail but it went into your "spam" folder or was filtered out as junk mail by your e-mail provider. However, if you are in the Disney reservations system, the discount information should be associated with your name. For that reason, when you call the Disney Reservations Center to make room reservations, it's worthwhile to make a polite inquiry. You might say something like "Would you mind checking to see if I am on the list for any room discounts? I'm afraid I may have missed a promotional e-mail." Don't bother calling about this if you have never stayed on Disney property before -- you won't be in the system.
