As you can see, opinions vary widely.
Haven't been to Sci Fi due to all the horrible reviews and the fact that scary B movies just don't seem an appealing dinner show (especially for a 3 and 6 year old).
Rainforest Cafes are fine. We've eaten at the one in DTD and in the Mall of America. The food is good, but I second the comment that if you have one near your home, go there. If you don't, might be a good option. My son was 4 at the time we went and the gorillas freaked him out a bit. We just went to the one in the Mall a month ago and he and my DD3 LOVED it.
We HAVE been to Crystal Palace for lunch twice and to 50s Prime Time Cafe once. We really enjoyed both. I thought the food was exceptional at CP during lunch and we are going back for breakfast this August. Plus, with little ones, Pooh characters are a must.
50s Prime Time Cafe was a great time - you have to feel like playing along or it may be a waste, though. I enjoyed the food.