We spent New Years Eve 2005 at Epcot and when we arrived it was almost at capacity. We got there around 7 pm and I was directed to park on the grass and was told it was one of the last 10 spaces available in the lot. There were pros and cons to the evening, but overall we had a great time. There was a dance party in the main area, just past the fountain and many families were dancing to current pop songs and wedding classics like the Electric Slide. As a fun extra, there were video screens set up that kept showing live images from Epcot Tokyo and other world wide Disney locations.
We didn't linger long in FW because of the crowds.
It was so packed that the CM's had formed a line to allow people to walk past the dance party from FW to WS. It was a narrow walkway and people kept stopping and blocking the path. My family made a human chain so we didn't lose anyone and laughed about it later.
It was less crowded in WS, however, it was impossible to get a drink which annoyed some of the group. The wait to buy a beer in Germany was over 45 mins, the line was outrageous. Once you got to the front, you could only order one beer per person so if someone had run to the bathroom (as happened to us) other people cannot order a drink for them. Nor can you order yourself 2 at a time. Still, it was only a minor issue.
We found an empty bench near Italy and were able watch the fireworks from there .. that was wonderful.
We waited a bit after Illuminations and it was practically deserted as we exited .. no one moves people like Disney! We found a dance party still going on in China and the kids got to dance to the last song. As we exited China, a CM in a kiosk gave us a few leftover flutes full of champagne!
We had a great time, though I don't think we would go back again on NYE. As I became more knowledgeable about WDW, I realized we were incredibly lucky just to get in that night because we came so late!