Simple tenses refer to time. Time is important. Below is a dialogue between a lawyer and a client. The lawyer uses "Did you" because she is looking for a specific date.
Sam: Did you ever see this film?
Pat: Yeah.
Sam: When was that?
Perfect tenses refer to the act. The action is important. Below is a dialogue between two friends who are picking out a DVD at the video store.
Sam: Have you ever seen this film?
Pat: Yeah.
Sam: Was it good?
Note that, for some speakers there isn't a difference between "Did you" and "Have you". They use them interchangeably. For example,
Ex: Have you eaten?
Ex: Did you eat?
To me, however, "Have you eaten?" means, I want to know if you ate, and not when you ate. And "Did you eat?" means, I want to know when you ate:
Hope that helps. :-D