We went to WDW the week before Xmas in 2004. It was beautiful, crowds were light. We made the mistake packing only Florida clothes and even threw our coats in the trunk at the airport thinking, "Hey we're goin' to Florida!"
It got down in the 50's, which is t-shirt weather in Colorado, but parka weather in Florida.
Also --make sure you have all your holiday tasks done before you go! We flew back in on Christmas eve, flight was delayed a few hours and alll the grocery stores were closed by the time we got home. Christmas dinner wasn't as it normally was-- We were stuck with what was in the freezer and pantry!