On my thirteen rides on Forbidden Journey, I noticed a few tiny details. When you enter the observatory section, you can see Harry and Ron's shadow while they're flying on the broomsticks. While the dragon is chasing you through the bridge, if you look closely, you can see the wing of the dragon behind the bridge.
Inside the actual land, near the bathrooms is an ATM machine that says, "Gringotts Automated Teller Machine."
Every single window display was filled with details, and was really neat.
Every 15 minutes, an owl pops out of the clock tower.