We just got back from our trip and were able to see the show on Saturday, the last night of our trip and the show's first night of public viewings. (There had been a night of AP previews and one of Team Member previews, too)
We had a good central viewing location by the Hogsmeade/Hogwarts signpost near the Frog Choir stage that gave a complete view of the castle as well as the surrounding trees. The show was cute, and I'm glad we saw it, but I wasn't blown away by it. I think "Celebrate the Magic" on Cinderella Castle did a better job of making it feel like things were really happening on/around the castle. (I haven't seen the new MK projection show yet, so I can't speak to that one)
As for logistics.... The shows ran every 20 minutes. It was quite evident that Universal was still working out some of the crowd flow aspects of trying to control the crowds in that part of Hogsmeade. The main bridge from Hogsmeade to Jurassic Park was a one-way exit out of Hogsmeade, but was open to people standing on it to view the show. They just had to have come from the Hogsmeade side.
The bypass bridge from JP to the front of Hogsmeade was open that evening, but hadn't been open earlier in the day. The little alleyway behind the wand shop was also kept as a one-way exit from the Hogwarts end.
They corralled the crowds in the front half of Hogsmeade. They'd let people into the Hogwarts end until the area reached capacity, then they'd stop everyone before Olivanders. (From that vantage point you can't see Hogwarts at all, so there's no spoilers if you're stopped there) Once the show was over, they tried to usher everyone to exit by either the bridge to JP or down the Three Broomsticks side of the main Hogsmeade street. Later on I saw that they'd employed the Disney trick of using lines of masking tape on the ground to show where people could and couldn't stand close to the Castle.
Now, the one interesting point of the crowd flow they have set up is that it essentially blocks off Forbidden Journey and Hippogriff from being accessed unless you approach the area as part of a show viewing crowd. (And if you're at the back end of the crowd, you're not getting to the attractions before the show) There were lanes kept free for people who were trying to exit either of the attractions without stopping to watch the show.
*However*, cutting the attractions off like this did have a benefit. On Saturday the park was open until 8pm. We joined the crowd around 7:05 and were let in to see the 7:20 showing of the show. When then show ended, we moved over near the stage until the crowd thinned out and then headed for Forbidden Journey. Despite the sign saying it was a 35-minute wait, it was virtually a walk-on. We were able to ride it three times in a row before it closed at 8:00. (For rides #2 and 3, there were so few Guests still coming through that they just closed off the Standby queue and sent everyone up the Express lane)
I didn't get a chance to see if there was one final projection show at 8 since we were still inside.
So, that was our experience. It may change as they learn things about crowd flow over these first few days and tweak their procedures, but that's what it was on opening night.
-Rob