Based on what I've read so far on these boards, I think that weekend is going to be pretty busy.
Here's what I've gleaned:
1. Friday, 12/16, is the local last day of school before Winter Break.
2. Locals come in droves Friday evenings (since some APs block out Saturdays), so DL gets crowded after noon.
3. Saturdays are always crowded at DLR.
4. The Christmas decorations/parades/snow increases the crowds (although not why my family is going, it's a big bonus!).
5. The 50th is making the above situations worse, as it brings happy people like us from around the world THIS year (my family doesn't make an annual pilgrimage, we are the suckers DL is targeting for the 50th!).
That being said, I know you can have a great experience by PLANNING ahead! I'd consider RideMax and definitely read HydroGuy's RideMax and FastPass posts:
See his FastPass thesis here:
http://www.disboards.com/showthread.php?t=885132
See his RideMax critique here:
http://www.disboards.com/showthread.php?t=885134
And make your PSs NOW! You don't have to plan every meal, but if you want to sit at sit-down restaurants (Blue Bayou, character meals) I wouldn't count on being able to walk up and get a table.
All this from someone that hasn't gone yet, but is deep in the throes of planning. . .

My two cents!
Have a great time planning and on your trip! See you at the park Thursday, 12/15!
D-n-C