When I went NYE 1997, all 3 parks (AK was not open yet) maxed their capacity by 10am that day. For fire and safety reasons, they could not allow any more guests in to the park, until enough guests left the park. When I made my original reservations, the CM forewarned me about this and told me to pick a park, make adr's for lunch & dinner way ahead of time, bring what I'd need to the park, get there right when it opened and not to plan on leaving, since there was an excellent chance I would not get back in. Again for safety and fire reasons, it does not matter if you have a park hopper or had your hand stamped, once the park hits it's capacity, they can't let any more people in. Around 11pm, I was near the stage at Disney Studios (near the hat) waiting for Kevin Bacon & his brother to perform. Panned my camcorder around the crowds and all you saw was a sea of heads in every direction, including all the way down the main street. After the fireworks at midnight, took over an hour & a half to get back to my resort.