Haven't seen any disney parks completely empty, but about a week before The Wizarding World of Harry Potter officially opened, a group of friends and I were in Orlando for vacation and Harry Potter land was secretly opened that day. It was busy during the day, but we went back about a half hour before the park closed to get some last minute souvenirs and it was completely empty! Unfortunately I forgot my camera that day, but it was one of the coolest experiences of that trip.
Empty Soarin queue...We were the first family of the day and had the ride to ourselves Picture is blurry because we had to move quickly before the rest of the rope drop crowd got there.