Just wanted to chime in to confirm basically everything that's already been said about the event on 7/28. We were staying at Coronado Springs and decided we wanted to hang out at the Poly for a bit, so we took an Uber there, then hopped on the monorail to make it to Magic Kingdom around 7.
Before the event officially started, we were able to ride Jungle Cruise, Splash Mountain twice, and BTMRR twice (using two fastpasses for SM and BTMRR,) plus grab a hotdog and a pretzel. Between 10-12:30, we did Jungle Cruise twice more, Pirates, Peter Pan, 7DMT, Pooh, Barnstormer, Tomorrowland Speedway, Astro Orbiter, Buzz Lightyear, and Haunted Mansion, plus hit 3 snack carts for 2 ice creams and 2 drinks each. A few of the rides we did, we normally would skip, but since there was no wait, we decided to give them a try. We skipped Space Mountain because it's just not one of our favorites, but I'm sure we could've easily squeezed it in.
The only ride that we waited even a little bit for was 7DMT, which had a 20 minute wait time listed, but was really only 15. I know a few people have seemed annoyed at that wait, especially after the glowing reviews from the bloggers, but that's the shortest amount of time I've ever waited for that ride, and unless you're lucky enough to get a fastpass for it, which I never have been, you're not likely to see a shorter standby wait time.
We didn't get any empty cars or boats to ourselves and we didn't see anyone staying on to ride again, so I'd forget that you read that anyone was able to do that. But we did walk right onto almost every ride and got a lot more done than we would have on a normal day in the park. The place won't be empty, but it will be a LOT less crowded and easier to move around and enjoy. And the temperature will be a lot more pleasant.
The lines for snacks were long when the event first started (we started in Adventureland,) but later in the evening they were very short. I don't think they ran out of anything. I saw a few people without lanyards an hour or so in, but after that, everyone seemed to have one.
We headed out of the park at about ten minutes till 1:00, caught the bus, and got back to CSR around 1:30. The bus was FREEZING. At one point I was debating whether I wanted to get off at a different stop and walk back to the room on my extremely tired feet, or stay on that freezing bus. Luckily we got to our stop before I had to decide. Seriously, bring a hoodie. Some of the rides get a little chilly late in the evening too, especially if you get wet on Splash Mountain or something.
Side note: I had scheduled our BTMRR fastpass at 9:15 deliberately so that we could ride it during HEA and see the fireworks from the ride, and not only did that work perfectly, but we were actually able to walk right back on and ride it again while the fireworks were still going, and it was awesome. If you've never tried it, you should at least once. I'm sure 7DMT would be just as good, but again, those fastpasses are hard to come by.
Overall, I wouldn't hesitate to spend the day relaxing out by the pool, then attend DAH, instead of a full hot day in the sun and crowds. I have really zero complaints. Just don't go in expecting that magical empty Main Street all night.