I used to work for Universal Studios Orlando during the grand Opening of Islands of Adventure. I was a roller coaster operator for the Hulk. A week before we opened, we had a celebrity day where Universal Invited a ton of celebrities to go to the park. It was mixed in with other guests though. I worked from open to close that day and My job was "celebrity escort." Just chat with them for a minute and strap them in the coaster.
The list could go on for quite some time, but here are a few highlights:
Steven Speilberg (who is creative director for the park. Met him more than once)
Jenna Elfman (coolest celebrity I have met)
Patrick Swayze (I was his temporary body guard)
Brittney Spears (I am so not lying. Strapped her in myself.)
All the boy bands
The list could go on. One small story: Steven Spielberg is deathly afriad of heights, so he didn't ride any of the roller coasters. But, since the Jurassic Park area is his baby, he had to ride everything. As you know the River ride has an 85 foot drop at the end. He rides the ride until right before the drop, stops the ride and climbs down a flight of stairs.