There is no difference in politeness. The tense can be important, depending on the context. For instance, 'what did you think of the movie?' would be really odd if you were.still watching the movie. You would have to ask' what do you think of the movie?' Otherwise, once the movie is finished, you can use either tense, as long as you remember that using the past tense can mean that while the person may have thought 'x' of the movie in the past, they can change their mind years later.

No, it doesn't! :)

Thanks, Master. :)

No difference. It feels the same if tense is not a factor. More polite: Use modal words.