If you have to ask how the crowds are, the following advice probably would be reasonable: think of the worst crowds you can fathom at WDW (MK) and then multiply that by two or three times. I have been to WDW five or six times during the Xmas holidays, and we have been as a family December 19-26, 1999, December 27, 2001-January 3, 2002, and December 23, 2005-January 1, 2006. The crowds on peak days (Xmas, NYE, etc.) are UNBELIEVABLE. If you don't like crowds, this is the wrong time to go. On the other hand, if you are flexible and patient this can be among the very best times of the year to go. We had a fantastic time this past year and the crowds were the worst we could remember. Go in with a good attitude and a flexible plan and you will be fine.