Heed Pixie's advice!
Since Christmas is on a Thursday in 2008 the conventional "week before Christmas" advice needs to be clarified. The crowd scale will skyrocket to 10 out of 10 the weekend BEFORE Christmas which will be 20th and 21st and be loaded to the gills through the weekend after New Years (also on a Thursday). Schools etc will not keep kids the week of Christmas so everyone will get out the week before. This strategy is also reflected in the "Unofficial Guide to WDW". Whether you like crowds or not, you should at least have a realistic expectation of what to expect.
We just got back from FW the true week-before-Christmas-Week-2007 and it really was nice and empty but the weekend before (as we left) it was filling up.
Do bring some lights or decorations for your camper/rv/site and you'll catch the Christmas spirit. Doesn't have to be a lot (some folks go WAY over the top).
I would also advise making your ressie ASAP if you don't already have one. Also, if the kids are younger and can afford missing a few days of school you can pull them out for the "true" week-before-Christmas-week" and have some low-crowd days.
Bama ED