Walking a reservation is calling and making a reservation that begins before your actual arrival date. Then you call back and drop the beginning night and add on a night to the end of the reservation. You continue to do this until you end up with the reservation you want.
For example, if you want 12/29/12 - 1/2/2012:
You would normally call on 1/29/12 to make the reservation. But because that week is so incredibly popular, and you want something in short supply like a standard view studio at BLT or BWV, it is very possible that you will find no availability because members whose stays begin before yours have already booked up those days. (They could start calling earlier than you because their stays begin before yours).
So instead you call on 1/22 and make a reservation for 7 nights. If you get that reservation, you are now guaranteed to get 12/29 -1/2 if you "walk" the reservation. No one else can call for 12/29 until 1/29/12.
But you can call before that to add nights to your reservation. So if the last night you really want is 1/1/2013, as long as you call on or before 1/28/2012 to add the nights of 12/29, 12/30, 12/31 & 1/1 to your reservation, you are guaranteed to get it. MS will also allow you to drop the beginning nights of the reservation - the ones you do not want.
The key to success is to get the first reservation.
Again, this is VERY SELDOM necessary. It only works for the 11 month window.
We are going on the Dream sailing on 1/2. 
