We went to Epcot July 4 '04. It was hot, but not sooooo unbearable. We just paced ourselves and took it easy basically. Had an early PS for Marrakesh, great meal. Food and service are always fantastic, and bonus was my 5 yo DD was picked to dance with the belly dancer. One of my favorite memories.
Worst of the day was our wait time at Test Track, with a Fastpass it was an hour and half! They kept shutting it down due to lightning in the area. They closed the stand by line and told stand by that ride ratio was 1 to 20. For every 20 fastpass holders, one standby person would be let on. Crazy!
The fireworks were phenominal. We had a group from all over the country, ranging from NY to Texas and places in between and everyone said it was the best display they had ever seen. After the show, they projected pictures onto spaceship earth, I wish I had gotten good pics of that. Very moving, I was in tears, my dad was in tears.
From where we watched the show, the pagoda in Japan, it was not crowded at all and before the fireworks we could see the fireworks from MGM going off. It was great.
I read on another thread that fireworks at MK were not so great, it was overcrowded and someone mentioned a fight breaking out.
I think Epcot absorbed the crowds much better and we were able to see and do basically everything we wanted.