Our experience 12/30/00 - 1/5/01
The parks were not nearly as crowded as we expected. We chose MK and - being AP holders,
DVC Members and staying on site - we expected little trouble delaying our arrival until 10AM (nothing was guaranteed, but I just had a feeling we would get in no matter what the situation). As it turned out, there were no problems whatsoever.
I'm sure part of it was the chilly forecast, but still, NYE was on a Sunday night, so there were LOTS of locals there.
The one mistake I made was not securing a dinner PS way in advance, but we got dumb-lucky and ended up getting one for the 7 of us at Cinderella's Royal Table in the Castle(!) for 8PM on NYE. Don't even ask how many times I called trying to get the ressie!

o)
We were able to book lunch (1:15 PM) PS for Tony's Town Square Restaurant at 10:15 AM that day! More dumb luck?
We checked with Town Hall several times to find out if the park was going to be closed for re-entry. Early in the day they could not predict if the park would ever be closed, but by 2PM they told us re-entry would be no problem. We went back to DVC via Disney bus (didn't want to take the Monorail and go through Epcot because that COULD jeapordize our MK re-entry status). After a 3 hour nap, we went back to MK and it was GREAT!
Overall, the only rides that had ridiculous wait times were Splash and Space, but with FP at least you didn't waste the time standing in lines. Also, we took the opportunity to visit and view all sorts of small things we either had never done before or hadn't for several years, which were all super.
We staked out our favorite spot (not telling where!) at about 10PM while the kids took turns going off 2 at a time to do AE and Time Keeper.
The midnite show was WORTH THE WAIT. I wouldn't have missed it for the world!
Good luck with your plans.
JohnG
Offsite 73,74,75,76,77,79,80, 82
Poly 82,83,85,86
Carribean Beach 87,88,89,90
Beach Club 91,92,93,95,96
Yacht Club 94
ASM 99
BWDVC 97,98,99,2000 (3 Times)2001 (New Year's for the REAL Millenium!)
DLand 74,78,84,88,92,94,95,96,98