When I went on it the first time, it was brand new. New Year's 1994, I believe. Apparently Eisner went on it a few weeks later and required them to shut it down and tame it down a bit. Mom opened up our trusty Unofficial Guide and said, "Don't worry it's just a movie." I was completely freaked out. I was 13, I was a wimp, and it was somewhere around midnight on our first night at WDW. My little brother was just under 11 and he really lost it, crying and screaming.
That being said, we both became huge fans of it later on. I think Stitch is stupid. When DH and I were there this past Christmas, we went on Stitch and I kept saying how much better Alien Encounter was. Oh well. Maybe they'll redo it again soon. All I can say is that Stitch had zero wait even at Christmas week. Alien Encounter would have a huge wait back in the day.